I cant say for atvs, I got got extra pipes and silencer that came with the purchase of the blaster. But have not used any of them yet.
But when I use to add pipes and stuff on my motorcycles. Aside from changing a jet screw and needle.
I mostly noticed, about 1 to 2 more hp. mostly at low end.
It really all depends what you want, for it to sound cooler, a little more ump. Either way, its usually better than stock.
FMF web site, if you use the fatty and core 2, recommend a 260 jet. they sell the kit. and info on the other setting on the carb.
I have a dozen different pipes for my KTM 125, serious, a dozen.
Engine makes 35-40 hp and I run it on the street, so I really get to wring the pipes out.
Some of them bring the power on low, but tend to taper off quick on top end.
Some of them are peaky top end screamers, with a powerband like a light switch.
Most of them mimic the stock pipe but raise the powerband 500 rpm. Not a big improvement.
My favourite pipe is my Doma, strong mid range, and yet still screams on the top. Not many work like that.
Pipes kind of push the power around, a bit higher or a bit lower, broaden it out or peak it up. If any pipe had a clear advantage over all the others, it would be the only pipe you would see on the track, because racers know. But you see, every racer has a different technique. Some just leave it on max revs and live with tire spin and loose back end, they like a peaky pipe with a sharp cut off to save the engine. Other riders stand back and like to feel that tire bite, riding on the torque and lofting the wheel out of corners, they want more mid-range and a linear powerband.
If you are new to 2 strokes, you probably don't want a maximum horsepower pipe, because that generally means it is an upper rpm peaky pipe and hard to ride unless you are "on it". As for the "pipe shoot-out" magazine tests, very interesting as far as the curve, but take the final hp figures with a grain of salt. A slight jetting change could sway the results several hp either way.
An important thing rarely mentioned is that for maximum performance the pipe has to work with the tune of the cylinder. Put a torque pipe on a max rev cylinder and they are pulling against each other.
There is an idea called "horsepower under the curve" that is all about what hp your machine can deliver as it runs through the rpm curve. Basically it means a 30hp machine that delivers 28hp over a 3000 rpm range will probably beat a 35 hp machine that delivers 28 hp over a 1500 rpm range. What it generally means for pipes is if you gain on peak, you lose under the curve.
So, is a pipe worth it? Well yes and no. If you are new to 2 strokes and Blasters, I think I'd advise to wait a while. Do the head mod, learn to jet, learn to ride. Figure out what you want in power and get a pipe to match. I bought dozen pipes to figure that out, you don't want to have to.
Jetting, head mod, squish, tires, shocks, and cylinder or port height would come before a pipe in my opinion.