Hi Rich,
The Umarex guns love RWS Hobby, and they're cheap as chips too. The lads who entered July's target pistol competition with their Smiths both used H&N Match Kugeln however, and Cookie got a very respectable score indeed with that combination.
Plenty of others, myself included, use Hobby in the CO2 section of the competition, so why not buy a tin of both and make your own mind up?
Hope that helps,
Mike.