Any tips on how best to take these puzzles apart?
For the 3x3 Mixup Plus start by taking out one of the inner edge pieces (the rectangles between the centre and the edge. To do this, pull one pair of corners on the top layer away from the centre while holding the rest of the top layer steady to make a gap between the centre piece and the inner edge piece. Tilt the inner edge piece up so that the tab clears the centre piece. If one face is too tight, try others.
For the Wormhole, remove the entire edge piece by pulling it straight away from the centre until the tab clears the centre and it pops out.
Note: the centres can NOT be removed until all the other pieces are removed. You will see why when you get it disassembled.