Owners of a male I bred and now a  puppy bitch who is having her first season at 11 months.

The male was fitted with the implant, and she is on day 13 of the season and he is showing interest. 

Obviously they are supervising.

In peoples experience how much does the implant affect libido.  will they need to totally separate them or will distraction and supervision suffice.

It's not 100% so they will need to be separated

Just like neutered dogs, they will still mate -but not as much. Will be fertile for up to 6 weeks after implant. When I had it done on one he mated twice but then didn't bother again.

My boy has the implant but wouldn't risk them being together when my girl is on season. He knows she is and the directions for Suprelorin state it's not 100%, so not worth the risk of keeping them together. Bit like our pill, not always guaranteed it won't stop pregnancy

Actually the datasheet for Suprelorin does NOT state it is not 100 % effective. All it says is that one out of 75 dogs treated and tested still mated and tied, but that did not result in pregnancy. Plus of course that the dog should be kept away from in season bitches until 6 weeks has elapsed.
http://www.noahcompendium.co.uk/Virbac_Limited/Suprelorin_4_7_mg_implant_for_dogs/-48969.html

Oh it was implanted 4 months ago, so supervision distraction and separation when not with them was the advice I gave.