Someone wrote a review on that mat on the Bed Bath and Beyond website. if you haven't already, for mildew removal, the review suggested sprinkling scouring powder and gently using a brush on the crevices. Worst case basis, get a new mat. Question: Did the mat get mildew despite hanging after every use?

Ha, that review was my own!! (albeit perhaps another pen name)
such are the quirks of the www, that you often get the same mimicked info, where people wind up quoting your own stuff back to you.
(I'm sure it's happened to me before..)

...and btw, i was very frustrated that the BedBath guys didn't enable people to edit, otherwise I'd have edited it to say that soaking in bleach is a much much easier solution.

But bleach is overwhelming (also see my OP for more re: that option.

So once again, can someone please advise
...based on experience, rather than the www?
(note the emphasis on expertise in my OP)

I went to the bleach-mold-myth site and that site is aimed at mold remediation on drywall and other porous surfaces. Your mat is not porous.

Personally, I would improve the ventilation in the bathroom and use a mild bleach solution in a spray bottle - maybe 1 part bleach to 9 parts water and lightly spray the mat after use.

Did you try the recipe for boric acid, hydrogen peroxide and water/vinegar suggested on the mold website?

Hi there, graywings, actually, I didn't, since I was too busy printing out the main page, as well as busy with a handyman doing odd jobs around here.

Thanks for bringing it to my attention, and for the suggestion!

I was going to try Arm & Hammer +Oxi Scum-Spray (just purchased) as well as

So now i'm thinking either the scum spray done outside with suction cups facing up, then tons of water dumped on it to rid the smell.

Then next attempt:
a crystal burst pak inside a painters pail (anything taller??) with water added. Then roll up the bathmat & dunk inside for awhile, followed by flipping the roll over for treatment on the other side, due to shortness of pail.

Then next attempt:
A vinegar/water solution inside spray bottle (what ratio?
OR:
Bleach solution inside painters pail?

The aforesaid article stating boric-acid is too hard for me. I want to try simpler first. BTW, thanks again - you're amazing - so often coming to the rescue!

You could soak it in the bathtub filled with 2 or 3 inches of water and cleaning solution or the clothes washer with some towels, or run it through the dishwasher.

I've had a problem with our mat getting mildew. Now after our bath or shower, I just hang it up to air dry. I haven't had any problems with mildew.