I used an SSBC kit to convert my '67 over 25 years ago.  My main complaint would be that they sold me an incomplete kit.  I converted from manual to power brakes and they did not include, not even mention that the brake pedals are different between manual and power brake cars.  As there really was no internet at the time it took me a while to figure this out.

Now, what's happened to that company in the past 25 years I can't say.  There has been a nationwide shift in manufacturing from the US to over seas.  Possibly if SSBC participated in that they now have quality issues.  Mind you this is purely speculation. 

They definitely stop much better than the drums did.  I can't say on other brands because I have no point of comparison.  The kit I got is a four piston caliper, not an exact reproduction of the factory setup, but very close.  At the time that's what I wanted, as the car was originally restored to be essentially showroom stock.  If I had it to do over again I'd use a completely different system, probably one of the Mustang Steve setups that lets you use later model Mustang parts. 

IMO a lot of the issues people bring up with brakes are actually installer errors.  More often than not the system doesn't get properly bled and there is still air in it resulting in a soft pedal and poor braking.  The best way I've found to bleed brakes is to use a clear vinyl tube from the bleeder to a cup or jar with enough brake fluid in it to cover the end of the hose.  You start at the farthest wheel from the master cylinder, open the bleeder, and start pumping the brakes.  You can see the air exiting in the clear tube, and the condition of the existing fluid in the jar.  Check the master cylinder every 20-25 pumps of the pedal.  You can't let the master level get too low or it will suck air in and you'll be starting all over again.  If you need to empty the jar just close the bleeder, empty it, and start the process again.  When that wheel is done just close the bleeder and move on to the next wheel in the bleeding order.  One of the best parts is that this is a one man operation. 

On old systems I bleed them until the fluid coming out is clean.  On new systems I go until there is no air coming out.  On new systems you may have to bleed all the wheels and then go back and bleed them a second time, or drive the vehicle for a day or so and bleed it again to fully purge all air from the system.  On a daily driver I try to bleed the brakes like this every 2-3 years.  Since I started doing that over a decade ago I've not had to replace a single caliper or master cylinder.  Moisture contamination in the fluid seems to be what ruins these parts.  The brakes also work perfectly.  If the fluid isn't good, and the brakes aren't bled right the best system in the world won't stop well.  I also advise on any new caliper or wheel cylinder taking the bleeder screw out and putting a little anti-seize on the threads.  This gives you the best shot of the bleeder loosening and not breaking when its time to bleed them in the future.  I also break the bleeders loose with a 6 point wrench or socket to avoid rounding off the hex.