Hi kirakat,
As you can see in the guidelines here … I would tend to avoid the major manufacturers or any mattress where you aren’t able to find out the type and quality of the materials inside it (see this article).
While durability may not be as big an issue with a guest mattress … you will still be able to find better quality materials in the same or lower price ranges than the materials that are in the Serta you are considering because both the Serta support foam and the pillowsoft layers are very low quality materials (see post #15 here) and would be a significant weak link in this mattress.
There is more about the “value” of a mattress purchase in post #13 here but outside of PPP (Posture and alignment, Pressure relief, and Personal preferences) which may also not be as important for a guest mattress because it isn’t for a specific person … a mattress is only as good as its construction and the quality of the materials inside it and if you don’t know this information then there is no way to identify any weak links in the mattress or make meaningful comparisons with other mattresses.
If you let me know your city or zip code I’d be happy to let you know about any of the better options or possibilities I’m aware of in your area and some of the lower budget options that are listed in post #4 here may be well worth considering as well.
Phoenix