I have a Jasper 400 and agree with bobj3. I find it easy to use for standard size holes and can be adapted for many routers.
What circle jig do you have at the moment?
How small a hole do you need to make?
The short comings of the 400 are that 1) not infinitely variable, only moves in 1/16" increments. 2) maximum size 7 1/2".
I also have a 'home made' jig based on the one made by Harrysin.
A circle jig is very handy to have.
I don't mind if other members disagree with my comments.
I don't profess to know everything, and I may learn something new.
"Never attribute to malice that which is adequately explained by stupidity."