A friend of mine who is a TMCC guru tried Legacy. He reported some signal strength issues on his relatively large layout that didn't occur with TMCC.
The Legacy signal, like DCS, is a two-way communication. I have heard (but not experienced) that Legacy may require a bit more tuning (but nothing as dramatic or problematic as DCS).
The signal propagation is the same but it is two way. MOST of the issues reported by the CAB-2 were false positives, aka a "warning light" when there wasn't actually anything wrong. The problem was in the software, the test for strength was way off. I saw the red light on my CAB-2 but also noted that whatever commands I was sending were working based on actual observation. This may have been an issue in the scenario of multiple CAB-2's and not all of them receiving updates on individual locomotives status. On a single CAB-2 layout this was not a real issue. I could successfully trigger sound effects and note they worked and I was able to visually confirm speed increases/decreases. I considered putting a piece of electrical tape over the LED so I wouldn't have to see it. I think a later version of the firmware fixed this (probably disabled the led on the controller
.I was never sold on the value of two way communication over the radio link. NASA routinely controls spacecraft where the time delay on two way propagation would be disastrous. Besides we already have two way communication. I hit the whistle button and the whistle sounds. If it doesn't, I hit it again. No need to tie up signal bandwidth and make the system even more complicated.
I suspect that the decision to not upgrade the CAB-1 had more to do with the pending demise of necessary CB-radio parts and trying to amortize R&D costs. It would also piss off a lot of users to find they needed to upgrade something to get it work the way it was originally supposed to but didn't because of a desire to get something out the door as fast as possible. The CAB-1 was designed to run PowerMasters, aka conventional trains with the TMCC stuff as a bonus. I suspect that the command stuff design wasn't quite frozen when they released the CAB-1/PowerMasters in late 1994/early 1995. The command base was almost a year later. This would account for the numerous deficiencies in the CAB-1 (address ranges, speed control, ...)