I have three bulk loaders, all bought used. I have a Watson 100, a Prinz 66 (copy of Watson 100) and a "The Daylight" which is similar to the Lloyd loader. They all work well, and I tend to keep one with a nice 100ISO film (currently Fomapan 100), one with a fast film (Currently Ilford HP5+) and the third with 'something else' (currently Kentmere 400).
Advantages? Well here in the UK I can cut the cost of each film in half. I can also decide to load a full 36 (or more) exposures or make a cassette with just 10. Total flexibility on how many exposures are in the 135 cassette. Due to the decreased cost, it allows me to shoot a LOT more film.
The Lloyd type bulk loaders are easier to use, but I find nothing wrong with the Watsons. I've never forgotten to twist the light trap open. To be honest, both designs work fine, and can sometimes be had for peanuts if you are prepared to bide your time on the online auctions.