I hate them, I do not like them. Sometimes you have to use them.
AND here is what i have observed.
Because of the offset, The toilet is now, and will always be prone to getting backed up
due to,,,er..ah..log jambs.
a few years ago, this was not an issue, because of tighter restrictions on water usage
it has become a large issue.
my advice on offset closet flanges, If you can, bust the floor and move the 90 over
then use a 4x3 90 and a 3'' collar inside the 4'' pipe, pack the concrete around the pipe,
to stop wobble.
if you have to, but only as a last resort, use your offset flange