20 is a sweet guage and don't mistake my comments to be any kind of a slag on 20 ga but, when it comes to any of the clays sports, if you get into it at all, you quickly come to the realisation that you'd rather pay for 12 guage feed than 20. That doesn't mean nobody shoots a 20 at the range, but it's much less common.
All that aside, I wouldn't hesitate to shoot any shotgun at a clays range. To test fire it, to torture test it, or to shoot trap.
I bought my daugher an NEF single shot 20 ga, modified, with a 22" barrel, and 12.5" LOP to learn to shoot trap. I shot some trap with it myself - to see if it shoots where it points, before my daughter tried to hit something with it. Eventually, I took it out in the field after grouse. Quite enjoyed it, too. Light as a feather to carry and quick to the shoulder like you wouldn't believe. Bit of a handicap on the fit, but not insurmountable.
If you have money for a variety of shotguns, or you've only got one, you still don't always use the perfect gun for the job. Sometimes by choice, sometimes not.
Someday, an Ithica pump in 20 ga. will be a collector's item, but not in our lifetimes. There's just too many of them. To talk about putting in choke tubes or having the choke opened up is going to cost more than a second gun (unless you know somebody).
In your shoes, I'd shoot it at the range and use it on birds. As soon as I could set aside a couple of hundred bucks, I'd get myself another gun (12 ga., 3" chambered, choke tubes - anything you want after that). Between the two, you'd have yourself covered for just about anything.
Watch out for the collecting bug, though. Questions like the ones you're asking are the first step down the long road of shotgun appreciation.
SS
