I like the 6 again rule, it is better than the game griding to a halt for every penalty. It used to be so stop start it was ridiculous.
But, there are tweaks it needs, what I would change.
1) Go back to 6 agains only outside the 40m line.
2) Stop handing them out willy nilly and I'd like to see the ref having some discussions with players and captains on the run. If slow in the ruck, or whatever give the captain that warning that if it continues 6 agains will start for it, get your team in line. Then if 6 agains start for it, at the next stoppage go speak with the captain and say I gave you a warning there and now we have seen some 6 agains for it, if that continues I may bin someone.
3) 6 agains should not be given for what the ref considers a professional 6 again. Deliberately holding down to get the line set etc on the 1st tackle should be penalised to make the penalty against that harsher.
4) Ref must call out 6 again and the reason. 6 again ruck, 6 again crowding, 6 again Pheonix etc.
5) I think refs have lost touch with when a player deserves the right to a quick play the ball vs when the tackler was dominant and deserves to hold down a little longer. Thats a feel for the game thing. and I see a lot of 6 agains given where the tackler isn't even trying to get up at all, or the tackler isn't really even on them anymore. Frivolous 6 agains need to cease and have them only for actual, clear infringements.
I believe 6 agains are an issue because they aren't an official penalty, and many of them only result in an extra tackle of two so are given way too freely. Much like Origin is Reffed, let the game flow, let teams get in to the arm wrestle with sets and earn the field position. Don't gift it to them with 6 agains.
I'd rather watch a game that is a contest between the two teams for ascendancy, vs ref chucking field position to teams for minor ruck issues.