I don't think 2 MOA is too small, at least not for a .22 caliber pistol. The trick is to find one with a clear crisp spherical dot. This dot needs to maintain it's concentricity and size through the whole variable intensity range. Usually the dot will distort at some point as the intensity knob is turned upward (brighter). Where this distortion occurs is what separates the good scopes from the not as good.
I can see some uses for a variable sized red dot scope but they are few. Here's why. In Bullseye, consistency is not just the name of the game, it IS the whole game. By varying your dot size you will change the impact point on the target because you are now varying the aiming point reference. This situation can be both confusing and frustrating to an unenlightened shooter. Now, I don't have to mention that frustration is a bad thing for a Bullseye shooter, it breaks down your concentration. Sometimes this same situation happens when a shooter just increases his scopes dot brightness and the dot visually increases it's size. I've had many a shooter scratch their head and wonder why the center of impacts had changed on the target. I'd ask them, "What did you change?" They'd say, "Only the intensity." Uh-huh! Now that situation may not make much difference in the 25 yard sustained fire strings, but on the long range line, a zero change can have a huge impact on the final score. And, if your shooting "Master" you don't want to drop a single point you don't have to.
The multi-sized dot scope would be best suited if you're going to use this kind of scope for a variety of shooting disciplines. But, you'll have to be sure and keep a good shooter's log for all your sight settings, to help maintain that "consistency thing". You should already be doing this (keep a logbook), for measuring your path toward improvement and the effects varying conditions have upon your shooting. (But I digress)
Beyond that, I can't really see a need for a multi-sized red dot scope. Nice option, but much will you really use it? And, is it really worth the extra expense? Only you can decide that! Why don't you make a list of what you really want in a scope and why. Then list your price range. Then do some in-depth research and try to match your "wants & desires" into the best your money can buy and still stay within the budget. Be honest with yourself, and I'm sure you'll be happy with the results.