I dunno- i think that saying there is less fold equity heads up is totally wrong, and check raising allin with the bare nutflush draw i think is a standard move for a pretty darn good reason.
Think about it- you are playing heads up with someone, and say they raise 3x the BB preflop, which they would do with anything from A3o to Q8s to AA. Realistically, its pretty damn hard to tell what they have when they make a standard raise, and anyone that claims to know is just talkin outta thier ass.
So the flop comes down
![The Five of Hearts [5h]](https://www.pofex.com/images/smilies/5h.gif)
and you have
![The Six of Clubs [6c]](https://www.pofex.com/images/smilies/6c.gif)
. Your opponent will make a continuation bet, and i think that a big checkraise or a push is almost always in order, because headsup there is actually ALOT of fold equity, since there is a pretty decent chance that either your opponent completely whiffed the flop and is just trying to take it down on a continuation bet, or that oyur opponent has a hand (lets say A7o) but he's not willing to play it for all his chips. The only hands your going to get called with in this spot are a J or an overpair, or a set of course, if your unlucky enough to run into that. Otherwise, your nutflushdraw is going to take it down over AK, 66, maybe even 99.
And, if it doesnt and you get called by a KJ, then you have three additional outs in the form of your ace, and have a pretty good chance of stealing the pot.
Even with the BARE draw (Assuming you dont have overcard outs, which you often do) you only need 15% fold equity to make that play since the flush will get there 35% of the time. I think with decent size stacks, you almost always have 15% fold equity, and thats why that play has become so prevalent.
The only problem is when someone makes that move, its so commonplace now that opponents may actually put you on your hand, and call you with a crappy pair, or even an AKo- i have a friend i play HU with pretty often, and he's a good player, a better NL player than I most likely, and i have called him with some pretty cheesy holdings in these situations and been right, because the allin checkraise, monstrously overbetting the pot, has almost come to mean that someones on a big draw. If someone had a set, theyd play it a little slower probly, and TPTK usually wont even play that fast- so mixing it up is key i think.
Anyways, i think the play is fine personally.