I was somewhat concerned myself about the side effects of polyethylene glycol (Movicol and Miralax) but have found many long time users on this forum with no problems so far. As I understand it, polyethylene glycol is not absorbed by the body.
Besides, I fail to see anything "natural" about magnesium-glycinate-chloride-lactate-carbonate-citrate-oxide-sulfate-hydroxide-taurate-threaonate. They've just been around longer.