I use the ES-1 with a used Nikon FH-2 filmstrip holder I got off eBay, and a Sony NEX-5N, a Canon 50/3.5 macro, and a bunch of old Nikon extension tubes so I can get all 16 megapixels of the Sony on the negative. The holder doesn't keep the film completely flat, but it's OK.
I use the Sony because I had it already, along with a Canon FD adapter, which is why I picked the Canon lens. The Nikon extension tubes I picked because they have 52mm threads, so I can put them between the ES-1 and the front of the lens because the Sony's APS-C sensor requires a bit more working distance than the ES-1 can give you.
The ES-1 has variable length, but it's a bit fiddly, so you have to handle it carefully between shots so it doesn't shift.
If I'm being very picky, or when I scan my MF negatives, I tape the negatives, emulsion side up (so the captured negative has its markings in reverse), to the textured side of some ANR glass I got from a local framing shop. I use Scotch Magic tape, and it doesn't seem to leave any residue. The glass pane lies on a light table on a copy stand whose geared column makes it easier to get the right focus and magnification. I attach an old computer monitor to the HDMI output of the Sony to get its live view output on a bigger screen, so I don't have to squint to ensure focus.
The other great thing about a copy stand is that I can make contact sheets by putting the ANR glass on top of the negatives in their PrintFile archival sleeves on the light table, and photograph the whole thing. It's not great quality, especially since the light table has falloff, but it's a good reference for deciding which negs to enlarge, so to speak.
The main problem I have right now is trying to replicate the richness of slide film. It's really tough to get something that looks like slides on a light table under a loupe. I'll probably have to do HDR to get it along perhaps with a brighter light source.
You can see some of my film scans here:
Film - a set on Flickr. The EXIF and comments should say which ones were scanned with the 5N. A few (some of the C-41 negatives) were scanned on a Noritsu by my local lab.
Good luck, and feel free to ask more questions.