I've used quite a few Sinars over the years--P, F, F2, A1, and P again-- mostly on location. They are very good cameras, but they are somewhat delicate. You have to be especially careful that lensboards and bellows frames are seated properly before pushing down on the locking levers. Never force anything on a Sinar! That is, unless your best friend is a Sinar repair man.
While I like Sinars, until you get to the P model I prefer ARCAs. (I've never used an ARCA M.) Any of the ARCAs are smoother, more ruggeded, easier to use, and in general slicker than an F2, let alone an F or an A1. The advantage of Sinar is the great availability of used gear, including stuff that no one else had in their line. Bellows, lensboards, extension rails are all available for reasonable prices. That can't be said about ARCA.