If you could Flash and still use the ult, well now that's just pure abuse. "Oh, what's that, I'm going to miss? Not anymore, I FLASH TO POSITION MYSELF LOL".
But either way that's just odd, never crossed my mind I could do that.
You could got warmogs and chain vest and still have more money and be tanky.
You could got Inf edge depending on game.
You could go triple dorans bf sword.
Triforce is good but is not worth how much it costs on gp.
Plus all these options leave more gold to buy stuff like orcale, wards or pots.