I have it for my Sinar F-1, and it is all I have.
It is excellent in that it GREATLY reduces the cost of your kit. DB lenses sell for peanuts. I have purchased five DB lenses beyond the 210 that came with the camera, and I have spent under $1,200 in doing so. Reputable E-Bay sellers specializing in photography equipment were the source for all of them, and they all work perfectly. I have a DB 90mm f/4.5 Rodenstock, DBM 121mm f/8 Schneider, DB 210mm f/5.6 Rodenstock, DB 240mm f/5.6 Rodenstock, DBM 240mm f/5.6 Nikkor, and DB 360mm f/6.8 Schneider.
They are also excellent in that they reduce the number of things that can break, wear, or be inconsistent.
They are convenient in that you can set slow shutter speeds down to 8 seconds.
They are very quick in that you never need to change anything on the front of the camera.
They are very precise in that you can always dial in f/stops in 1/3s (and can easily position the needle in between the thirds, even).
They are great in the same way that a Speed Graphic is great: If you can mount whatever glass it is to a lens board, you can use it (unless, of course, it is simply so big that the opening for the shutter cuts into the image circle...like my c. 1850 Voigtländer Petzval).
They are great for chronic accidental exposers in that if you use the second cable, you cannot accidentally leave the shutter open and then pull a dark slide. (I never use this cable myself; too much crap running all over the place, and provides too much resistance when inserting a film holder.)
They are not great in that the lenses can only be used on a Sinar.
They are not great in that their top shutter speed is '60 (unless you get the significantly more expensive model).
They are not great in that if the shutter fails, your shoot is over if you are shooting short exposures. (You can still shoot with flash or long exposures if they fail. Open the shutter, or, with DBM lenses only, remove it entirely if it is jammed shut, and use a lens cap, film box, hat etc.)
They are not great in that DBM models, which are far preferable IMO, are harder to find than DB models, and when you do find them, they are often older and in worse shape. With the DBM lenses, you can set the aperture without needing to have the shutter attached. I have gaffer taped both of my DBM lenses to other cameras. This would be impossible with the DB lenses, unless I was shooting wide open.
It is not great at all in that the front standard is moved quite a way back compared to when you use the same lens in a between-the-glass shutter. This bunches up the camera quite a way when using wides. With my 90mm lens, a bag bellows is not only necessary for movement, but necessary just to focus on infinity. I have also run in to situations when using the 90 in which I am physically prevented from making the swing I want to make, because the standards are too close together. For these reasons, I would say that wides 90mm and shorter are a weak spot for the DB system. Additionally, this makes the front standard more unstable when using heavier lenses, like my 360 and 240s. I prefer to use my P front standard when using these lenses, instead of my F1 front standard (which is the relatively flimsy Multipurpose standard).
It is not great in that no matter how fast your lens is, you cannot use it any wider than f/5.6. If you really want to make a shot wide open, you can remove the red screw-in post on the back of the lens so that the lens will open up all the way. However, with large format, the real advantage of fast lenses is on the ground glass, not for the shot itself.
They are not great in that they take a proprietary synch cable.
So, when all is said and done, here is the way I look at it:
The DB system allowed me to get into a very full kit very quickly for a very small amount of money in the grand scheme of things. It has never failed to work as it should, nor do I have any reason to think it will, other than the fact that in life, things never do. This is simply me accepting Murphy's Law, though, not stating that I have any problem with the quality of the equipment itself. When the Sinar is called for (the emphasis is key here) in my "work", I have all the kit I need for 90% of situations, and I got it all for $1,200, plus the trade of an inherited guitar that was in the best case scenario worth $800. So, $2,000, camera included, $1,200 of which I actually had to pay. Additionally, I have put another $500 or so into roll film backs and a rotating 6x9 gizmo. (Everything but the rotating gizmo is usable on any Graflok-backed camera, however.) For the tools that I have at my disposal, $2,500 is horribly dirt cheap.
However, the drawbacks of the DB system are indeed large drawbacks in much of my "work". I am seriously lacking in the lens department on my other 4x5 systems. I have everything I need for the Sinar, but very little for my Speed, my Technika, and my Kodak No. 2 5x7. I miss being able to use the terrific glass on my other cameras. Outdoors, I miss fast shutter speeds if there is any wind. So, in the end, I am slowly going to end up duplicating these FLs in between-the-lens shutters.
Using the DB system is like having all your eggs in a basket; It can be a good thing if you want to make just one trip to carry all your eggs. It can be a bad thing if you need to walk across a rocky stream to get those eggs where they need to go, and thus a backpack is really the better tool for egg transport in the situation. It is the perfect and most economical solution if all of your "serious" 4x5 work will be done with a Sinar. It is a great solution for somebody who shoots in studio with flash, or interiors, most of the time. For anything else, you start running into its drawbacks fairly quickly. It is not unusable in other situations by ANY means, but the drawbacks do make themselves apparent.
So, IMO, definitely go for it if you don't shoot any other systems. Go for it if you want to assemble an extensive kit for very little money. Maybe go for it if you shoot outside, but only if you are OK with having '60 as your top shutter speed. Do not go for it if versatility and interchangeability to other cameras are key things for your "work". Do not go for it if a lot of what you do involves making a lot of tilt and/or swing movements with extreme wide-angle lenses.
