Hi earlybird,
I think that most of my comments would “echo” brass’ comments. As he mentioned I would always make sure that you know the quality of all the materials in any mattress you purchased because most of the Zinus brands tend to use some lower quality/density materials in their mattresses which would be a “weak link” in the mattress in terms of durability.
A forum search on Vivon (you can just click the link) will also bring up more comments about them.
A forum search on Night Therapy (you can just click the link here as well) will also bring up more comments about them as well.
They both use memory foam that is CertiPur certified* (and see here* for each brand as well) but of course are also shipped compressed from China (see post #6 here) which outside of the use of lower density foams can also have some effect on the durability of the mattress.
ADMIN NOTE: *Removed 404 page link|Archived Footprint 1:certipur.us/pages/find-a-foam-supplier/zinus-2/|Archived Footprint 2: certipur.us/pages/for-consumers/find-products/ & replaced with latest CertiPUR link
The best place to start your mattress research is the tutorial post here which has all the basic information, steps, and guidelines that can help you make the best possible choices … and know how and why to avoid the worst ones.
I have no problems with anyone posting any links on the forum as long as they don’t link to a company that someone would benefit from or has a direct or indirect interest in (with the exceptions that are mentioned in the forum rules).
A google search on 10" night therapy memory foam will bring up several 10" Night Therapy mattresses and several sources for them but I’m guessing that the MyGel on Amazon you meant is here and there is also a non gel 10" Night Therapy here on Amazon as well although I personally wouldn’t consider either of them or any mattress that included lower quality or unknown materials.
Phoenix