More and more, my game is a mix and match of 1E and OSRIC.
I let the Players use the OSRIC PHB section to create new PC's on their own, I just have to get final approval but otherwise, It's all there for them to make PC's while I'm not home. Actually, it's easier for them to use OSRIC than to let them use the 1E PHB to do it.
That's pretty much the bulk of it right there. I also let them use OSRIC for the "shopping" list when they are considering purchasing something. Again, the DMG and I have the last word on it, but it's usually pretty good.
My players are 12 and 14 years old. They have looked for info and descriptions of things in the 1E PHB and compared them to what is written in OSRIC equivalent. Both of them find OSRIC easier to understand, more clear and less ambiguous.
I don't really use the monster book section very often at this point. I stick with the MM1 and my own home brew monsters more often than not.
in terms of the DMG section, I might use it more if I were to print it out. as it is, I have my 1E DMG constantly open and flipping from section to section. Same with the PHB so I can remember how to handle spells the PC's or NPC's declare.
Because I do have the DMG and PHB right there at hand and not being snagged by the players (Cuz they have the OSRIC pHB section) I really have no need to print out the other sections. save on ink and paper.
But to be perfectly honest, If I were to be getting back into things now not having my old books at hand, I would be full fledged OSRIC, no doubt in my mind.