Dublin to Orlando
 

Flew Business Class first time with Aer Lingus on Tue 22nd Feb.
Excellent experience with very good choice of food and Cabin Crew were so good at all times.

Incidentally clearing Immigration and Customs at Dublin, also, for the first time was so quick and effortless.

Arriving in Orlando and no more TSA hassle on arrival.
In fact as we were technically a 'domestic' flight there were no checks on arrival whatsoever.

It's the way to Go and Arrive.

I was looking at them as a way of getting Bristol to Chicago in the Summer. I'm confused what kind of seat they offer. I know it's flat but is it horizontal or inclined?

IMHO any person in the UK that has not got a direct flight to America should seriously consider using Dublin or Shannon because one will clear American Immigration and Customs much quicker and little or no hassle.
Of course it depends on getting a suitable connection from the UK through Dublin or Shannon.
The Aer Lingus Business Class seats whilst not fully horizontal are nearly so.
Tip - press the 'snooze' button more than once to get maximum horizontal.

On arrival did you land at an INternational gate or a domestic gate. Wondering if Aer Lingus use Terminal 5 in Chicago now or have they moved elsewhere.

At Orlando Aer Lingus are using Domestic Gates 30-59, Airside 3.