Be careful if working with biological fluids (p.e. serum). These kits tend to co-purify big amounts of circulating soluble protein agregates along with the exosomes.
Dear Joseph, the main problem of the common commercial kits used for exosomes isolation is that do not discriminate between different EVs populations but co-isolate different EVs populations. The result is a very protein-enriched pellet. If you want to use a commercial kit to isolate exosomes from your sample, i suggest you to check and exclude the presence of other EVs populations by using a size exclusion protocol (TEM, NTA, etc.) and/or WB.
If you have any questions, please feel free to ask.