Your positionals on Gekko and Kasha are each worth 64+ potency, which is quite high as far as positionals, other than (Leaden Fist) Bootshine are concerned. But, it's just those two.

The less obvious disadvantage is that SAM, unlike those with normal, direct positional bonuses, will never have a decent reason not to bother with a positional; whereas others' bonuses might be overkill anyways, effectively leaving you free to finish off an enemy from wherever, SAM will want to get that extra Kenki regardless.