While I enjoy my Agfa Isolette V, a 6x6cm folder without a rangefinder, it's far from a substitute for my Rolleiflex and Yashica TLRs. I consider it more like a high grade Holga or Diana, fun for snapshots and arty stuff.
Even adding a Rowi accessory shoe rangefinder hasn't helped as much as I'd hoped. The Rowi is calibrated in feet, the Isolette in meters.
Also, the Isolette's focus ring isn't entirely accurate or...what's the word? Linear? I can either calibrate it to be accurate from 1 to 10 meters and not worry about infinity being quite sharp, or set it to be sharp from around 5 meters to infinity and not know whether anything closer than 5 meters is truly in focus.
If I wanted a *serious* MF camera that was also lightweight I'd get a Mamiya 6 (the recently discontinued version, not the old folding camera), wide angle lens, have Mamiya refurbish it for reliability and use that as an alternative to my TLRs.
There are some good old folders with uncoupled RFs and the really high zoot Voigtlanders, but I can think of better things to spend money on. For $250-up I'd be seriously tempted by the new Cosina-Voigtlander RFs and a really good wide angle.