Open source products are out of the question as well (If you don't have the necessary knowledge), you don't know If these are secure enough and whether they contain backdoors or not.
using open source software is never about "you" personally having the skills to review it. nobody has the time. for example we are using bitcoin-core but most of us might not even have looked at the source code. the point of open source is that the source is open for everyone to see and if the project is popular enough you can be sure that others have reviewed it specially if it is sensitive and deals with lots of money, and then you can trust it doesn't have any backdoors.