Those are meant to run HVAC stuff, totally different class of pump. I bought one some years ago to run a mini vacuum fixturing prototype, I will say it did better than I expected it to do, but it certainly does not move enough volume for brakes. No system is perfect, with the hydroboost if you toss a belt or have an engine failure you're out of luck as well (I guess, same as the stock setup). Does it have some sort of accumulator so you get one or two more assists without the engine on?
Just left to run, it heats up in a hurry. But as I said earlier, in a normal stopping scenario, it only runs a second or less to catch back up. I am sure if you just sat there and pumped the brake pedal continuously for a while you could kill it, but that's nowhere near a normal operating scenario. I've thought about buying another pump to see how long it'll chooch continuously before burning up.
The health of the vacuum system would be paramount though - if you've got a leak and it's running frequently to compensate for that, that's going to be a problem. There are gotchas with this that do make me apprehensive about selling anything related to this at all. The idea of getting sued because someone wrecked their rig after burning up a pump because that vacuum leak "wasn't that bad" makes me wonder if this is a good idea or not.
When I bought my truck I found a brand new Motorcraft pump but decided to pass since I was spending a lot of money elsewhere on it and hadn't diagnosed the system yet..probably don't need to tell you that's $90 I really wish I would have spent, hah.