Hi rjar,
It would depend on the specifics of the mattresses you are comparing. Making brand comparisons isn’t really that meaningful and the only way to make meaningful comparisons between mattresses is on a mattress by mattress basis. Of course the suitability of a mattress in terms of PPP along with the policies, benefits, or options that are part of a mattress purchase from different retailers or manufacturers would also be part of the “value” of the purchase and your personal value equation as well.
I can tell you that all of the Sovn mattresses use high quality materials and there are no obvious weak links in any of their mattresses but to compare them with another mattress would require knowing the specifics of each mattress you are comparing.
In general terms … the Spruce uses a 6" 100% natural Dunlop core and a 100% natural Talalay comfort layer 9which I believe is 2") with a high quality cotton/wool quilted cover so this would give you a reference point for comparisons with other mattresses.
All of the manufacturers you are mentioning tend to be more transparent (although Restonic may only be transparent about some of their mattresses and not others) so there are no clear “cautions” here as far as brands but I would make sure that the retailer is willing to provide you with all the information you need before you go there because otherwise you could end up spending time testing a mattress that you really like and have no way to know its quality or durability or how it compared to other mattresses.
There are no shoulds and shouldn’ts here because it’s really a personal choice and would also depend on what you were most comfortable with, your “risk tolerance” with an online purchase, and how they compared with your local “finalists” in terms of your personal value equation.
Phoenix