Considerations about equity apply equally well to HU play as to full ring. However, the main difference is not the number of outs you have, but that HU you're not too concerned about whether they are to the nuts or not. Small flushes are often good. And whenever you have any decent draw you'll be pushing it hard.

Yes, definitely good points.

Some other exceptions on calling with draws: 1) You have some outs but also feel like you can bluff a lot of additional scare cards (good against players who bet fewer draws), 2) You have very good implied odds (good against players who can't lay down).

i thin kthe idea of pot odds is really much less of your EV in HU. it's still important, but not as important as in a loose-passive game.

your comment on implied odds is key.

i'd also say that accurately valuing fold equity can make a HUGE difference in win rates for HU play. the check-call flop and check-raise turn play with air can be a big money maker (although it increases variance).