Curious about RRS BT Pro and RRS SC-LR for the Atlas BT65CAL for ARCA rail, any good?, how about the Arca Rail In general, better the Picatinny in rigidity?. Was looking also at 419 ARCALOCK, like the idea of their mechanical locking feature, but the ARCALOCK Rail is a little pricey. The RRS clamp is compatible with both Picatinny and Arca dovetail .