Rack units are often designed not to require seeing or touching during performance. A MIDI-controlled Looperlative LP1 or two, synchronized Gibson Echoplex Digital Pros would do well for the sight-impaired. Yesterday, 12/11, Steve Uccello wrote that he's selling his LP1, with a MIDI pedal.
Two Looperlative LP2 pedals or two TC Electronics Dittos (or one a TC Electronics Flashback for reverse, delay, and some looping), with an analog signal switcher (the other kind of looper), would also work.
The advantage of two LP2's is that you would have four assignable foot switches. Each could be dedicated to a single function prior to or during performance (e.g., reverse, 1/2 or 1/4 speed, replace, retrigger). The LP2s can be MIDI synced.
The advantage of the Ditto is that it is designed to be controlled solely by a tap pattern on a single foot switch. You could hardwire a third switch to the pedals' switches, synchronizing them.
I believe that the Boomerang's rotary, function selector does not have stop pins. This could cause problems for the sight-impaired during live performance.