What is Reddit's opinion of Dime Bag Hardware Inline Axle Aluminum Speed Spacer 8-Pack Spacers for 6mm Axles Roller?

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What you pointed at there are spacers to not have the wheel touch the frame. Those are necessary, I’m guessing your axles are thinner than the wheel bearings and standard sized spacer you have in the middle. You’ll need this Dime Bag Hardware Inline Axle Aluminum Speed Spacer 8-Pack Spacers for 6mm Axles Roller https://www.amazon.com/dp/B003AOGJ3A/ref=cm_sw_r_cp_api_glt_fabc_8G9G5S7G4FZZQW0J100F?_encoding=UTF8&psc=1

Reason I’m guessing this is what you’re needing is because the spacer that some recreational skates have aren’t the standard type. These go in between the wheels and inside the wheel bearing opening for a thinner axle screw

Yeah, the little discs are bearing spacers (specifically, those are "floating" spacers for 8mm axles - these sleeve-type spacers are for 6mm axles), and they go in between the bearings in the middle of the wheel. If you already have spacers in your wheels, then you don't need to worry (unless you were on 6mm axles before). The smaller black bolts are the frame bolts (to attach the frame to the boot), and Seba/FR uses 5mm bolts while most of the rest of the industry uses 4mm, which is why they probably don't fit in your non-Seba/FR boot.

Seba, FR, and a few other other skate/frame makers use one-sided "speed" axles that thread directly into the frame instead of a second axle component. This means you only need one allen wrench to open them up.

Joey Mantia recently did a video on frame positioning. It's from the perspective of a speed skater but the advice he gives applies to most other skating disciplines. It should help you figure out the best position for your frame.

They work as intended. Their job is not to let you to sqeeze two bearings of one wheel together when you tighten the axel. You install one bearing, then spacer, than second bearing. Even such https://vsrv1assets4.gtp.com.au/clients/s/surfsailaustralia/largeimages/968342.jpg spacers will work.

Regarding bearing types. There are two types of rollerblade spacers, designed to work with 6mm and 8mm diameter axels. You bought spacers for 8mm axels (more common), hope your skates have 8 mm. There are also 6mm axels and spacers for them (like this https://www.amazon.com/Inline-Rollerblade-ALUMINUM-SPACER-Spacers/dp/B003AOGJ3A) they are less common and used mostly on some cheaper fitness skates.