If I remember correctly only difference between the 2 is the more expensive of those two choices is actually OMRI listed for those Uber picky organic peeps! I used the cheaper of the 2 personally even tho everything else I use is all organic I didn’t think these really mattered! Also 5 million is plenty for that many pots but if u have an outbreak I’d suggest getting the 10million count since only like $5 more! The more u start with faster they can go to work knocking out infestation! And way they work is they burrow into the body of the gnat and eat and multiply inside and once consumed they bust out and that new lil colony moves on all now looking for their own food and continues process always multiplying while outbreak exists! And I was bug free since applying mine in September and was literally 3 weeks or so ago I had the fungus gnats in the 2x4 but the pots in big tent that were treated never got any! Hell I transplanted 4 from the 2x4 into those big pots but still haven’t had 1 gnat in the pots with the nematodes and predator mites!
I did have some other bugs living in my straw mulch where the nematodes couldn’t get to them so I used some captain Jack’s to kill them off which in all likelihood killed off what was left of the mites I applied but nematodes did their job and kept me fungus gnat free!
If u call that arbico place to make an order if u wanna kill em off really quick they can recommend a pest spray that’s organic that u can use as IPM to spray plants to keep bugs away but also in the meantime can water it in to kill them things off muy rapido without harming any beneficial bugs or microbes in your soil! Lost coast plant therapy is a good 1 I know of and they actually offer small sample bottle for just cost of shipping which is like $6! It’s like 4oz which is enough to make 4 gallons worth so should be enough to kill off all gnats before u use it up!