Newer hardware revisions with similar specs are merely to reduce cost. LiteOn does it, Samsung does it (AB is old, FB is new with small buffer), LG does it (90 is older than C0, C0 has small buffer). Except for the part where Samsung sometimes has firmware issues, and LG reduced the number of available write speeds, quality shouldn't be majorly different. (But to that end, slightly older drives would probably be a tiny bit better, if only because of mature firmware).
Buffer size: whatever software buffer size you were using on a drive with a 2 MB hardware buffer, should work for a drive with a 512 KB buffer (data is flowing too quickly for a minor 1.5 MB difference to matter).
For LiteOn's iHASxyy z nomenclature (example: iHAS120 6), the z tells you what hardware revision you had. (z is a number or letter from 6 to 9, then from A to F, with a few extra hardware versions Y, X, and W that fall out of step. 6 is oldest, F is newest). When you say you had an older model "04", that doesn't indicate which hardware revision worked for you (those extra two or three digits only indicate how the drive was bundled/packaged, and/or for what market it was packaged).
Drives aren't the same thing as drivers; be mindful of that if you ever need to troubleshoot things.
Drives have been making rings on discs ever since 4x and 8x drives came about, as a result of them using Z-CLV to step the speed up progressively. Actually, burn rings can happen with any drive that recalibrates during burning, even using CLV (flat lines, where the data transfer speed is constant) or CAV/P-CAV (curves; the data transfer speed smoothly increases as the laser progresses toward the outer edge). So you could well run into the rings with older good drives as well as this LG you'll receive. It may not look appealing, but it's the nature of the burn process.
Lasers decay due to use. Like most electronics, excessive heat will shorten the expected life of a given part, but it can also be affected by the initial quality of the part. ...And, much like other mechanical and electronic devices, they may well age even when not in use, though that's not typically a major problem unless it's something that involves potentially reactive chemicals (such as some types of capacitors & batteries).
Older drives sometimes produce better burns. But, as exemplified by your iHAS124...A? Y? B? C?, having an older device doesn't guarantee fewer issues.