I had two such sales in the last half year (1 on Squadhelp, 1 on Dan.com).
So far so good. SH name is now fully paid (6 instalments, but there were 2 late payments at the first 2 months, but later the buyer always paid on time). Name sold on Dan is always paid on time, but there has been only 2 instalments out of 17.
I'm pretty sure one or even both sales would not have happened without instalment option.