Has anyone built and flown one of these carrier planes? Just curious as to how good or bad they are.

I built one about a year or so ago and haven't had the chance to fly it yet. I agree on the over engineering but it looks like it will take a bunch of abuse. What were you using for an engine?

Is the G-S Bearcat the basis for the Brodak profile Bearcat kit?

My first Carrier Profile was a GS Bearcat built in 1979. I was very fond of it, and recommend it to a sport flyer or Sportsman competitor. I used a Tune-Hill plain bearing .36, which had lots of power (more than the K&B 5.8, IMHO) and it flew very predictably with that, getting high speeds in the low-19 second range. The structure was, I thought, very well engineered and really, really tough, so a very powerful engine (think Nelson today) would not be a problem for it. The only serious modification was to add an internal line slider. This was within the fore-aft limits of the tip rib, so it only moved a few inches and would allow hanging only on a really calm day. It was not really ever set up to compete with the 4+ minute low speeds that are common today. However, on a windy day, it was way better than a modern airplane in terms of stability and reliability, although not nearly as slow as required for modern competition. At one contest in Milwaukee the wind was 55 mph (combat models were being blown out of the sky, and forget about stunt...) and the Bearcat did manage a high, low, and landing.
The landing gear was stock and never broke the wing in a hard landing. That wing was well designed. That's why they included that silly cardboard for sheeting the center section. The strength comes from a really carefully built spar system. When you look at it you can see sheeting would add very little strength to the wing structure even if it were much stronger. (It's not really anchored, and it has squared-off ends, which would provide a bad stress concentration at the leading and trailing edges if it were really strong.) But I just couldn't bring myself to put cardboard on it and replaced the cardboard with 1/64 or 1/32" ply. It's only purpose is to give the pit crew something that will allow them to hold the airplane by the wing.
I would recommend this for the sport flier, the Sportsman flier, and the Nostalgia flier. It regularly competes in Nostalgia very successfully and would be great in Sportsman, since the landing score is the most important one in Sportsman, more important than high or low. Dick Perry won Profile in the 1978 Nats with one, and I won with it in 1984 and placed second several times. I think I am looking forward to building another one if I ever get the time, and might even try an electric version.
Pete