It depends on the player pool. It's a naturally good "pre-adjustment" if people tend to call too much against 3-bets, for instance.
2 -> 7/8 is standard, and the fact is that 2 -> 9 is small enough of a change that even if we presuppose 2 -> 7/8 is "ideal", then 2 -> 9 is going to be a slight mistake at worst.
Whether 4-betting 3x your 3-bet is bad depends on the size of your 3-bets and the SPR. Like, at 2 -> 7 -> 21 (100 deep here and henceforth), it's clearly fine, but at 3 -> 10.5 -> 31.5, I don't like it at all, because it makes play for the BB easier -- although it can be fine against people who haven't faced it before and don't naturally hit upon the correct response. Anyway, I've already "hinted at" too much, maybe, so let's leave it at that.