Anyone study the options and care to comment? I'm looking to dump traxxas starter assembly.

Don't use a drill. Get a rotostarter or similar. The nitro-specific rotostarters aren't as strong as a drill and as such not as likely to cause damage in the event of a hydraulic lock.

If your OS uses an external one-way clutch bearing like the Traxxas engines do, you might be better off with a pull starter or looking into the rotostart system from a Losi 350/3.4 engine. I just don't know if the Losi 3.4 uses an internal or external one-way clutch bearing.

An OS .21 will probably do fine with a Pullstart. If you're able to pick up on what it's perfect priming habit is, you could have it down to a one-pull start. That's how I have gotten my 3.3 TRX engines to since I swapped to Pullstart from EZ-Start.

YMMV.

It appears Roto start has been discontinued.

Try Sullivan Products Tiger Drive, pretty sure its the same one that fits the TRX 3.3 engine.
Sullivan Products sent me one back in 2012 to try as they hadn't tried one on the O.S 21tm engine, it fitted & worked well. I used a cordless drill with cut down allen key, turned power of drill down so not to spin engine to fast or risk damage.
Here's the website. Product Index

Thanks. Looking at the rear facing Sullivan s702 model.

Use a cordless drill with a torque clutch, (most drills have this) set it to correctly and you wont damage anything.

May do the side deal, the engine angle allows for this. Apparently the one way bearings has to be pressed on further for proper fit and alleviate the damage some have complained about in the past.

Or just get the Revo starter box.

I didn't think the rear one would work as the rear arms etc were in the way so you couldn't get the shaft onto the roto start, it might though, been a while since I had my Revo.

I have a hpi rotostart on mine. I used the one for the hpi 25 nitro engine. Swapped the external one way out for the one from the 25 as well. So far so good with that set up.