So far I’ve tried: Discipline, Balance, Anarchy and Feral. Neither Future nor Truth have particularly powerful combat heroes or T1 units (Spectral Hound is great in some matchups, but terrible in others, Glaxx is ok, but KotC is terrible in this deck). So far, I’ve found I basically always go for Future tech II, so tech II units are not really a factor. I’ve been trying specs which have strong T1 units, and an impactful hero early. Also, I’m not a huge fan of either Blue or Purple starters, so that has an impact too. Other specs I’d like to try are Necro (very strong T1 units, Garth is not an amazing early combat hero, but skeleton spam could give you the board presence you need to set up T2, and his spells are really good) or Strength (Rook is arguably the strongest hero in the game, and has good spells - T1 is pretty awful though). I’d also like to give Discipline another go - it was the spec I tried first, and I’ve learnt a lot about piloting the deck since then.
The deck looks impressive when you can pull off the combo, but the major weakness is that you’re often paying 6g and a card (Tech II + Omega) to set up a threat (18 hasty damage for 6g, or 27 for 10g, more if you have another Omega in hand) which generates no actual board presence. Opponents who go all in at Tech I can usually capitalise on that and leave you in a position where you can’t keep Tech II up (you can see this in my casual games against @cstick and @Mooseknuckles - for links see Anarchy above and here).
As is often the case with Codex strategies, it’s easy to get caught up with the combo you’re trying to use, and to tech/play/spec cards which will make it even better. Instead, you need to concentrate on getting the combo in place, because it’s usually powerful enough by itself to end games.
ETA: links