Closet Flange with FERNCO or Not?!

Hi there, looking for some advice on connecting a new closet flange to a 3" copper soil stack / waste pipe. I am helping family members get an older house ready for resale and want to do the job inexpensively of course but I also want to do a fair and reasonable job for the future owners as well.
All that being said, I have removed an old closet flange and surrounding subflooring from the bathroom. I have a 3" copper soil pipe with plenty of access around it from above and below, this stack also extends vertically approx. 12" so there is material to work with. I was told I could purchase an ABS closet flange with metal surround (sorry of my lack of incorrect terminology - I am learning as I go) and connect it with a clamp of some sort. So I subsequently purchased an ABS flange of this sort with a FERNCO coupling that has two metal worm-screw type banded clamps, one on each end of the approx. 4" length of rubber Fernco. The guy at the plumbing supply place did not really want to sell me this, he suggested replacing flange with another copper flange. However, that piece would not cover the needed rise between where the copper soil pipe has been cut off in order to meet the level of the floor / new flange placement. He also expressed concern that this setup may leak eventually.
What I would like to know is;
1. Can I use this setup effectively?
2. As the home will probably have a home inspection before sale, will this be a concern? (Does it meet code? State of CT.)
3. Also, should I scrap this idea all together and get a new piece of 3" copper pipe to solder in to the stack pipe to connect to a brand new copper closet flange?
Thanks all in advence for any input, I will try to post pics early next week if they would be helpful, and the site is great, I have learned more here on home improvement skills than any other resource!
Erick

Normally when it's copper to ABS, I go with something like this.
Each side of the rubber connector should match for pipe size,
You can get
Copper x ABS
or
ABS x ABS

They have metal surrounding the rubber, to prevent pipe shifting.

Thanks for the info Terry,
Is that Proflex by Fernco as well? I have read in other threads people mentioning couplings VS. the Proflex...? Am I correct in my guess that what I have purchased is a coupling? It is more of a sleeve, whereas what you have pictured has more support built in with the metal running the length of the piece? The Fernco I have does indicate it is made for Copper to ABS, and both are 3". But somehow I am just not trusting the purchase and want to be sure before I install it and find out later I should have done something different?
Thanks, Erick

The fernco without the sleeve is only for use underground...
Above ground use requires the metal sleeve...