Fernco and Mission fittings? Questions?

A few Q's ref. Mission and Fernco fittings:

1. Web claim that some local codes forbid using Fernco in the ground. Is this correct?
2. Claim that Mission fittings with draw-bolts wont always nip up enough?
3. Claim that Mission have thicker walls and better SS wraps than Fernco?
4. Splitting wraps, rubbers and worm-drives between Fernco and Mission can create a better fitting?
5. In residential work, which brand would the forum favor
for installing where and why?

6. Are the above brands all-rubber traps and bends etc. now legal in most codes?

I've just noticed previous posts that deal with some of the Q's i asked above. Sorry about that.

The Fernco neoprene sleeves are not permitted aboveground. The reason is they do not hold the pipes firmly enough to prevent movement. A banded coupler has a clamp that covers the entire sleeve thus making a firm joint. I don't know if there is a particular brand favored or not. The clamps on the Fernco sleeve tighten just fine, they are essentially just like the hose clamps on you automobile. As far as I know, the rubber traps and bends are legal, but they are not used by real plumber, legal or not. Flexible PVC drain connections are definitely crap.

1. "Fernco" is a brand, not a specific type of coupling, but when most people refer to Fernco, they mean the rubber sleeve with hose clamps on either end. Those are the ones that are not permitted above the floor anywhere, and not inside the building in many areas. Their "transition" couplings which use gear bands on either end ARE approved.
2. A worm gear tightens around the circumference of the coupling, a coupling with draw bolts pulls tight on a tangent to the coupling which can leave a "loose" spot under it.
3. Competely irrelevent.
4. Quote; "Splitting wraps, rubbers and worm-drives between Fernco and Mission" I have no idea what you are referring to or asking.
5. whatever my supply house stocks. I would not waste time searching for one or the other.
6. Completely illegal, and even if they were not it would be a bad idea to use them.

Thank you both for the replies.The "tangent" explanation especially.
#4. "splitting" is referring to stripping down a fernco and a mission to make one "good" fitting. I now have the answer.
#6. why is it "bad" to use them?

hj, if i understand you, Fernco "transition" fittings that c/w "gear bands" are permitted above ground/inside a house?