I've always liked the whole cat/pigeon combo.
1. Do you have any dependents, who would rely on your insurance? (Diving outside training will invalidate this)
2. Does your personal travel/medical insurance cover any gas mix
Other than that, its your lookout. If you're the sort who's capable of self training and are able to be commited enough to do this including ALL your research, then go for it. Theres more than one way to skin a cat.
You need to be able to answer the following though, before attempting a committing mix dive;
You're diving to 70m for 30 mins.
- Whats the ideal drive gas
- What are the ideal bailout gases (Mix and free gas volume)
- Whats your SCR and OC deco schedule
- How will you handle breakthrough at depth
- Your drive gas is 10/52, whats your loop running at a SP of 1.3
Theres loads more, but this is a good starting point
The reality is that the in water skills probably represent more of a challenge.
For the record, I've no axe to grind either way. I think theres merit in both options.
/Zak