Reball's will set you back a bit of cash 1st off. But in about 5 months they would have paid for them selve's. Trust me on that one.
They are a great training aid, they help training no end.
Reballs are to be used indoors mostly. Outside you will either loose them very quickly, or you will loose them very quickly.
They do not casue damage to the guns, only the barrel sometimes due to if they have been use for abt 8months they sometimes can get a bit rough.
We have at lest 12,000 and we use them every saterday for 12hrs training.
Any one that say's there not a good training tool, wel i wont tell you what i think of them.
There not a rip off tbh, reball we last for ever....