I'm an AK newbie who's acquired a MAADI MISR S/A

I want to replace the PistolGrip, GasPiston, and Century FCG .  I'd like to do a U.S. slant brake too, but haven't decided yet since the threads are turned.  I've searched around and seen whats available from Tapco, Global, K-Var, RedStar, RPB , SKSParts and couple others  found via Google.  I have a couple of purchase questions.

-Are all gas pistons created equal? Is the $19  one as good as the $30 as the $40 or is the $40 just a marked up $19 piston?

-For the FCG, the options seem to be RedStar, FSE, and G2.  The adjustable RedStar is a little over my budget, but everybody loves them that I've read.   Are there other brands I should consider?  How does the FSE and G2 compare?  Are these really "drop-in" or do they often require a little grinding,smoothing, etc to get it right.  I would be new to messing around with the internals  and it makes me a bit  nervous.

-Are there any sellers I should stay away from? Any other sellers I should look at?

Thanks much!

As far as I am concerned a gas piston is a gas piston.  I've bought them from Tapco and K-VAR.

The RSA is expensive though I got mine from www.sportsmansguide.com/ when they carried them at a discount. I haven't installed it as I am saving it for a new gun.

The Tapco G2 is a good FCG that I have in 2 rifles and it can be bought from a member here in the equipment exchange for less than Tapco is currently selling for shipped.  Scottgull