I went from a Etec 250HO to a Merc 250 Pro XS on my boat this past spring. Diamond Sports did the swap. Was not bad at all. Expect to have to buy a few cables and such and you might have to replace some gauges in your dash. Maybe a new throttle cable as well. Just depends on the boat itself. I had the Level 1 Merc Monitor installed.
The dream is free, the hustle is sold separately.