If I remeber correctly the 06 Nytro seat is the only seat that has the correct wiring to work on a rx1 tail light, since they used the same tail light. I know the seat will fit and guys were using them on the RX1,s. Some guys ordered the nitro cowl so they didnt have to cut there cowl(tank cover) but its a pretty simple mod either way.
I know the Apex mountain seat is fimer foam than a regular apex or attak and I think the nytro was firmer as well.