Of course the Rolleifix only works with a Rolleiflex TLR, not with other MF TLRs or SLRs.
Like the others said... If you put a heavy camera on a light tripod then it's not very stable. Most TLRs aren't much heavier than 35mm SLRs, so I think you'd be okay, unless you were using an exceptionally light tripod. MF SLRs get pretty heavy.