1/ Because they hold their voltage at a higher current than alkalines, hence more power to the servo under high servo loads.

2/ They fit the stock battery holder.

3/ They are rechargeable (I added a charging jack to my Savage so I wouldn't have to deal the radio box cover....RTR25)

4/ They are cheap, and avialble locally at many stores such as Wal-Mart, Grocery Store,, Canadian Tire etc, and are often on sale too.

5/ If one battery fails, you only have to replace it, not the whole pack

6/ Performance is great. Maybe my steering servo would be stronger with a 6 volt rechargeable pack, but I havn't seen any performance issues so far.