I don't know why they even bothered with the 1 xp cost. Even if you manifest only Throw Ectoform with all your PP every day, you still won't manage to fall behind more than one equal level encounter's worth of xp, assuming 4 encounters/day. Like all small xp costs, it either costs you nothing (since you never fall into the small xp point where your allies level but you don't) or you're behind for one encounter and get net more xp because xp is a river. The only way to make it more than a rounding error is by slowing your game down terribly (to 1 encounter/more than one day) or by spamming it with a recharge loop.
Numbers:
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Psion 3 has about 18 PP (11 base, 6 Int, 1 race or higher than 18 Int or whatever), 6 xp spent/day. Each encounter gives 900/4 xp = 225 xp, so it takes 37 days of spamming this to cost an encounter.
Psion 10 has about 140 PP (88 base, 40 Int, 12 race or higher than 26 Int or whatever), 46 xp spent/day. Each encounter gives 3000/4 xp = 750 xp, so it takes 16.3 days of spamming this to cost an encounter.
Psion 20 has about 500 PP (343 base, 120 Int, 37 from items or rounding or higher than 34 Int or whatever), 183 xp spent/day. Each encounter gives 6000/4 xp = 1500 xp, so it takes 8.2 days of spamming this to cost an encounter.
On a side note, you get about 40-50% of an encounter's xp extra for being down a level, if I remember correctly.
[/spoiler]
Other than that, it's a short-duration Mirror Image. It's great if you can buff up beforehand and walk in with a dozen clones. It's less impressive if you have to use it in combat. On the upside, Extend Power plays really nicely with Throw Ectoform. I'm sure there are other shenanigans you can play, but I'm not the most creative person.
