I'm the owner of Michell and I use Incognito RB300. I opted for it since I already had RB300 unmodified from my previous TT. The sound is great but SME309 is more robust and adjustable. Very often precision matters more than rigidity. If I didn't have Rega arm I'd go for Willson Act.05 or Kuzma Stogi arms. They combine rigidity of Regas and adjustability of SME-s. BTW Kuzma/Michell is known to be one of the best TT/arm combos.
OL Silver vs SME 309
If you had a choise of these two arms for the same price, which would you opt for to go with a Michell Gyro SE?