Wales Capital Region let a 12-0 lead slip as they lost their cup semi-final to Sale Sharks and dropped into the plate.
But they won their next two games against English giants Northampton Saints and Harlequins to leave the Ricoh Arena with silverware.
John, who spent several years as a coach with Wales 7s, joined Richard Hodges to lead the squad and he was pleased with the way his charges learnt and developed during the high-octane tournament.
He said: “It was a tough start. To go 10-points up against Sale Sharks, we had really put ourselves in a position to win the game but 7s being 7s there were a couple of turnovers and we lost out.
“But from there the boys bounced back really well. There was a good performance in the semi-final against Northampton and to beat that Harlequins side was a great achievement.
“We scored some cracking tries, defended well and our kick-offs were good – we learnt as the tournament went on.”
The Blues squad was made up of core Wales 7s players who have previously represented the region, academy youngsters and 7s specialists from regional clubs.
They clinched victory at the death with Declan Williams and Johnny Lewis making the inroads for Aron Wyn Evans to cross.
John has paid tribute to their never-say-die attitude and reckons the experience will be beneficial to the young guns.
He added: “I’m sure when Harlequins scored with less than a minute to go , people thought that was it.
“But we knew we would have one more chance and we capitalised on that. Declan made a great break, Johnny Lewis took it up and kept it up and Aron just went for the line and got over – job done and a great way to finish.
“The squad had a good mix and they got better the more we played together, we only had two short training sessions but they gelled really well and learnt through the tournament.
“It’s great for the boys, particularly the youngsters from the academy, to play against Harlequins, Northampton and Sale – top quality Premiership teams.
“The fact that they performed so well against those teams should give them confidence.
“The standard of the tournament was really good, Danny (Wilson) and Jockey (Matt Sherratt) came up to watch so it was also good for the boys to play in front of them.”