I'm using 2 at the moment.
I recently pulled the no-peep off my Mathews and placed it on my Patriot since the one that was on the Pat was placed on the Tribute- it's like a regular old swap meet at my house.

I was shooting the Pat without it at 30 yards and that I was doing good until one group of flyers made me break out the wrenches.

The good thing about one is you don't have to look at it, but it's nice to use it to check that you are being consistent if you want to. Draw, anchor, glance up make sure it's right, aim and shoot.
If you don't want to look at it- nobiggie, you'll still hit the target.

The first doe I shot last year Idon't remember looking at it at all and still squared her true. The second deer I was at full draw and anchored when for some reason I checked it and sure enough the odd position I was in had caused me to torque the bow without realizing or feeling it. Imade the needed correction (a slight twist of the wrist) and then let the arrow loose-> paydirt. It would have probably landed just fine if I didn't correct the situation,but since I had the no-peep to check I know I did my part and let the broadhead do its.

There not for everyone, but I like 'em.

BTW, you can usually find a used one since they are a love hate item. The haters make good sellers