Could be a variety of reasons why they have low comp (maybe they got a good deal on some low comp pistons or something), but you're right, it can be sluggish. On the other hand if they have low comp, it can allow you a slightly larger tuning window.

It's a give and take on either scenario:
low comp - easier to tune, slightly lower power
normal comp - in the middle
high comp - well, you get the idea

low comp is usually the novice tuners' choice. read up on it more