What "special" Augments work best?

Now, doesn't the bio converter kill you eventually unless you find a health box, or what?

Bio-converter's downside can be completely negated by a tech passive. Rank 6 of Team Support, the bottom evolution, "Life Support" gives you 200% health regen and +50% Health regen cap, for 3 seconds after using a tech power.

Have a couple of tech powers on your list, use a tech power at 50% health or so, your health is fully refilled. Unlike many of the other passives in this vein, there's no internal cooldown timer for using it, so each time you use a tech power you regen a large portion of your health.

This, to me, makes the Bio-converter borderline broken, and one of the most OP things in the SP campaign. I don't personally like it, so I don't use it.

Edit:

For the record, if you're gonna go Bio-converter Pirahna, Isharay, Dhan or the like, using cloak, turbocharge and energy drain is probably the strongest power build you could have.  Cloak with added damage and the 2 second extention to cloak for the extra shots, turbo charge for a huge DPS buff, and energy drain to refill shields as needed...you have 2 tech powers to refill health, 2 powers to boost damage, and the best shield restoration power out there, unless you just really like Charge.