In my Solo 2350 powered 29E, I find it quite possible to recognize a thermal even though everything is vibrating and the vario readout is very nervous.. I try to circle with a constant speed and if the vario constantly is positive and I still have the impression (seat of the pants input) I'm in a thermal after 2 or 3 turns, I shut off the engine.

Of course only if situation (altitude, landout situation) permits.