I too am a little sceptical of the benefits of pre clearance. I assume all the US bound airlines will have to shuffled to operate from the same terminal. Then a need improve transfer pax experience to the US terminal.
Then given the nature of MAN, add on the US queue time to the already lenghty bag drop queue, the security queue. Then the airport will want to ensure plenty of duty free time- they will be asking you to check in 4 hours in advance. The cost of the operation would barely justify the benifits.
Then this US sterile area will be empty for 16 hours a day.
I've passed through ATL many a time and immigration has varied from 10 minutes to an hour, which isn't that different from arriving into MAN. I've also done the DUB pre clearance, that was OK with no queue - but,when I used it, it was a single flight- hardly the case at MAN.
Re the Austrian service, from what I can see the lowest available fares are over £300 return, so it is hardly going to be a "winner" when you can still book with Lufthansa with one stop for half that amount. Given the flight times, there appears little advantage of the direct service.
Jet2 3 x a week service I suspect will not be affected by this new service, this also runs in at about half the Austrian fares.(but obviously without the interline options)