FYI I used this facility to go to the USA recently - I'd say it's definitely worthwhile outbound to the USA - passing US immigration took all of of 2 minutes TOTAL from leaving the normal transit area and at the start of a trip it was well worth the 2 hour lay-over
On the way back you don't get any benefit and have a 2-3 hour connection before onward travel into UK or Europe so no real benefit.
In a perfect world I'd go via Dublin outbound and come back direct
EI Business was good but not exceptional - limited food choices but good IFE - their newer A330s with staggered seating are better than the older ones tho'