using both remvi and assault turret?

I did at one time for the achievement's. It's effective but not mindblowingly so. Maybe more so when they've got all their points.

I'm thinking set the turret to cryo ammo, vi to missiles for detonation, I could either go with a primer/detonator like overload, energy drain, or incinerate for my third ability, or maybe that overcharge combat ability that buffs your weapon

i opted for cryo turret and Beam VI and i detonate with overlaod.
I use rifles for damage but i could use any other weapon.

The Mastermind cheevo was actually one of longest cheevos for me to get, as they're both pretty boring powers to use and I kept switching back to my biotics.

In NG+ you could mix them with the soldier profile, and thus play a full power soldier with more allies.  The soldier profile doesn't actually do anything for combat powers, so there's no real reason you shouldn't shop around once you've got the spare points.

I'm not playing a full engi but a tech soldier (no! not an infiltrator!), so I had 2 profiles.

First one for mooks : engineer profile for tech construct bonuses and defense drone (damn rushing mooks)
- Concussive shot : good for detonation and roleplay purpose (tech soldier)
- VI : good tanking with engineer bonuses, laser is fine on shields, and primes for tech combo
- Assault turret : cryo ammo is good for crowd control on unprotected enemies

Second profile for heavies (armor) : soldier profile for more DPS (assault rifle)
- Concussive shot : not so great on armor, but detonates cryo combos (or anything my companions prime), also useful to knock back heavies
- Turbocharge : for even more DPS
- Assault turret : cryo ammo is good for debuffing armor, and cryo combos once again

Thats a good idea. I'll try it out.

The nice thing is that, Assault Turret being in both profiles, you don't have to repop it (and wait for cooldown), it stays as you switch profiles.