Yes, I use a 903SWC, first with a P25 and now with a P45+. Couple of points,
1. As a hand held carry around camera it's scale focused, so unless you're shooting at infinity quality will always be compromised to some extent by lack of focusing accuracy. That said, used with the P45+ and cropped accordingly, it's probably as close as I'll get with digital to one of my favourite film cameras of all time, the X-Pan!
2. The cabling feels a bit primitive, but it works okay.
3. You can get surprisingly accurate framing for a 37mm x 49mm sensor from the standard 903 SWC/M viewfinder.
4. I sometimes use mine for interior architectural shots because of the Biogon's virtually zero distortion, but for this application I always the ground glass back for precise framing and focusing.
5. The 38mm Biogon always suffered from quite marked vignetting, for some reason this seems more obvious with a digital back than it did with film.
6. If you're getting a 903 then avoid the very latest 905, Zeiss were forced to reformulate the optics when a certain glass type was discontinued, and the results are inferior to the original 903. Also avoid any models with the spirit level built into the body. The very early ones aren't coated, and the later ones with the spirit level in the body can suffer from a problem where the shutter bends slightly and brushes against the glass caused micro scuffing. Actually the 903 from the very last year where the spirit level is in the body was probably the finest 903 ever made, but to keep it simple just look for any 903 where the spirit level is in the viewfinder rather than on the body!