Let me tell you about my experience with my Smartech Spider, aka, Firehammer. I paid $425 U.S dollars for it on ebay. It is durable, I have never broke a part yet, although I did need to fix a few problems that require some mechanical knowlegde. The differential gets rocks stuck under it causing the outer sleeve to spin and sling grease out. I fixed it by making a fiberglass diff cover, problem solved. Next is the pinion, and spur gear get munched by rocks, so I made a back plate out of aluminum on the gear cover to keep rocks out, problem solved. It won't matter if you buy an FG, Smartech, or any other large scale with an open diff, these problems will be the same. Now with that said, you can have a fun 1/5 scale to drive if you are willing to fabricate some of your own modifications to make it reliable.
If you want the best in 1/5 technolology, the Baja 5B is what you want. My brother bought one after I got my Smartech, and it is a better design than any other 1/5 out there, but what ever you get, the best power upgrade is a tuned pipe. I put a Jetpro on my buggy, and it gave a huge power increase.