I noticed that there are 2 different model numbers of Drylok Extreme, model 209101 and model 28615 (at considerable cost difference). Both, I believe, are Latex-based and 5 gallons. What's the difference in the products? Is one much better than the other or contains some antimicrobial materials?

I'm considering use for waterproofing basement walls (Cinder block) after etching with Muriatic Acid.

Reading the product overviews at Home Depot you see that the more expensive version is much more comprehensive, and has more applications and rated for a higher hydrostatic pressure protection.

From what I saw, Home Depot only lists 1 of the Drylok Extreme model numbers and not the other. Home Depot also lists the regular version (which aligns w the description that u indicate).

My look up showed both

DRYLOK 5 Gal. White Extreme Waterproofer-209101 - The Home Depot

Look them up separately, and you will be able to compare them both. Possible that your location won't list one as it also notes extra fees for shipping to some states.

It also notes it can't be shipped to me, but must be picked up at another store.