That FRER definitely looks darker. So this is just my two cents: the Walmart test looks almost identical to the $ store tests I've used, with the little hole for dropping the fluid onto the test, and the pinkish-purple lines etc. I wonder if it's exactly the same test strip, just with a different casing?
I learned my lesson with cheapie storebought tests this cycle. I had spent so much on FRERs by 13-14 DPO that I decided to get a bunch of $ store tests and use those for progression since I was taking so many tests. Well my $ stores started getting lighter at 13-14 DPO and I FREAKED out. Was certain I was having a CP, cried quite a bit. I decided to confirm the CP with FRERs, went out and bought a pack. To my total shock, over the next day, the FRERs continued to get darker while the $ stores were still getting successively lighter.
So I personally think the best tests for progressions are FRERs, first and foremost, and Wondfos second. I used Wondfos for progression with DS and they were just great. I would not worry at all that the Walmart tests aren't getting darker--I would be reassured by those FRERs
See post #15 to see what I mean:
https://babyandbump.momtastic.com/pregnancy-first-trimester/2350859-progression-2.html