Ideally have a go one one before you buy one, that will give you the best feel for one obviously!!
But they are very light, small, and pretty quick. I personally am not keen on their trigger pulls, but that is personal preferance, i much prefur my egos pull.
They are very gas hungry as stock, and ideally need a lot of upgrades, but these are fairly pricey, but a HE bolt kit will get if up to a decent level of efficiancy.
The one
here for example has ALL the upgrades and utterly rips, also the seller is a nice guy and a m8 of mine
Shockers are a heck of a lot of gun for your money, but before you go spending £300-400 on a marker, i really would try a few out before, as i had about 5 markers before i settled on the one i prefured the most, which cost me a fair bit in depreciation!!