HA trains only DR and OD as secondaries.
1 on 1 is almost as effective as one-position HA training with JS added as a bonus. If you will create true PGs without any shooting abilities, this will hurt your team.
1 on 1 training is great also because you can use it when on of your trainees doesn't get full 48 minutes. With two trainees, getting them 48 minutes on PG isn't an issue, but with three trainees anything can happen. From injuries until end of the game to fouling out.
To prevent this, every game try to put one of your trainees, who doesn't play at PG spot in a certain game, on SG as a backup. This way he will log 12-16 minutes as a SG, so if he will lose some minutes on PG spot due to injuries/fouling out, he will recuperate them at SG spot when you change your training from one-position to 1 on 1.
It works the same for big ones (ID or IS - change to RB).