[DarkPira7e]

I've seen plenty of good blocks with goofy installs, plenty of good blocks with good installs, and a couple blocks with bad machining from them. Read their recommendations and follow them to the T. Especially head gasket thickness, recommended oil weight, start up and break in procedure, etc.

Make sure the builder is someone who understands the FA series of Subaru engines; it is not like the EJ.
Any low production engine block service is likely to have some jig or machining issues once in a blue moon; just be in close contact with the builder and ask a lot of questions and make sure everything seems good (deck clearance mostly) and you should be good. The more " built" an engine is (closed deck, bored, sleeved, etc) the more points of failure you're introducing.

The closer you stay to stock measurements, the more likely you are to be safe from machining mishaps

I have one sitting in the room I'm typing this in. Should be going in within a couple months ( I hope). I watch several IAG blocks get installed on EJ and FA cars monthly at a shop I help out at (not an employee, I just do menial tasks for them since they're close friends of mine) Very rarely have there been issues, but I will say that getting IAG to cover something with their warranty is nearly impossible.

Edit: If you don't mind discussing it, why do you feel that you'd like a built block? Unless you've put a window in your block, I'd suggest having a shop tear your current functioning engine apart and just replace the pistons/rods/bearings in accordance with your power goals. A block from a company like IAG isn't inherently stronger; you're paying for them to install and machine stock casehalves to fit. A lot of the cost of the build is casehalves (that you already have and can re-use unless you put a hole in it from some sort of failure)