I have some IKEA vanities and they are extremely particular about the placement of the p-trap. The p-trap has to be very close / parallel to the wall for the drawers to not bump into the p-trap. I've modified the drain rough opening so that the p-trap will work and the change in direction is close to 180 - is there any problem with that?
That appears to be fine, though I would agree that an additional picture from a different angle would be helpful. So long as the relationsip of trap parts is maintained, all the rotational freedom they have can be used to make them fit.
I would choose a trap with screw connections, rather than what appears to a a "glue it and hope you never have reason to regret that" but both are acceptable for code. Once you have the experience of having to take a saw to one rather than just unscrewing it, you might come to agree with me. If it's not a 2" trap inaccessible under a concrete floor, I want threaded connections.
It makes absolutely no difference. To illustrate why, let's break down the individual changes in direction by 90° segments through the trap, beginning with the vertical drop out the tailpiece:
None of this changes when you swing the trap pivots. It's always exactly the same sequence. While a fluid dynamics geek could argue the finer points of the forces involved, the variation is negligible for purposes of an unpressurized drain.
