I have used MAQS and find them to be effective overall, especially if temps are monitored during use. Too hot and you will have problems.
Oxalic acid is most effective during broodless periods.
I am somewhat concerned with the number of people that seem to be using Oxalic frequently, say once a week for 3 weeks, etc. While I don't have a problem with that specifically, I am amazed that folks are using something that in many cases is not approved for use in a bee colony. "Washing" frames etc. may be a cute way to skirt regulatory law, but heaven help you if someone gets sick and you are found to be using something not approved for use in your colonies.
I am also concerned about the number of folks that use Oxalic with honey supers on their hives. Even when Oxalic is approved for use (it is here in Nova Scotia) it is not approved for use with honey supers on.
I suppose if you consume the honey yourself the risk is minimal, but if you are gifting or selling it I would be extremely concerned.