Using Grens for about a week with 5 engines down and 6 unlocked. Never have quite enough GBE, but it's pretty successful.
Have to say I like Sparky more than Kavan. UR any def at beach that is bad, like a boom can and the passive critters really help keeps the RL damage down.
Only real negative I can give is that the trained pool is not so big. I burn them up getting the chests with very few opportunities to continue unless I diamond train.