@Aquanaught
From TM site.
1. O-ring pack.
For the same reasons that
@Siebter said. I had to change only one oring in 9 months, on my CU.
2. Long stem.
I didn't like the short stem, and never use it. Glad I got the long stem.
3. Universal WPA
This was my game changer. TM through water is a BEAST!!!!! You can also use any extra cooling pieces, j hooks, drydrotubes, basically anything with a female adapter. Since getting my WPA, I rarely use my CU. And cleaning is a breeze.
From other sites,
1. Extra batteries.
Having 3 batteries in rotation was enough for me.
2. A good battery charger.
Do not overlook this one. My first ebay crappy charger caught fire. Got a nitecore i2 now.
Sorry, I'm not tech savvy at all, so I can't provide links.
Good luck. I'm sure you'll love this thing.