Ray I've ordered the Saito 1.2 for this one. I did consider the OS but the reviewer on the Pac Aero site had problems fitting his OS 1.20, besides I think the Saito muffler will fit better inside the TM's cowl. Strangely the manual recommends .90 or even .70 four stroke but the dealer strongly recommended the 1.20 and the TM can use the extra power.
I bought mine in a shop in London and they only had the red/silver one so I never had the choice. I think the yellow looks neat also.