Been using 4.5.2 for a while now, and have not had any issues. Have not tried opening saved games with older versions of scid after adding comments with the new one, but I wouldn't think comments from a game file would pose any problems. Since you have a copy of each on different computers, you'd likely be able to test out fairly quickly though. My guess is, you won't have any problems. If you don't like the new layout, scid is fairly customizable...just make it look like the old one.
Good luck!
Anyone using this version??? I put it on another computer to try before committing. Initial screen format remindes me of ChessBase (I have the older trail version) Haven't had time to get serious with it.
One initial question. If I edit a game in 4.5.2, add comments & run the Stockfish anylisis engine (save the results to the game ) will I be able to open the same game with and older version of SCID. Same concern applies to Repetoir & Tree Masks.