> There is no reason not to use both.

Fear of it not being as reversible as it was supposed to be would be a pretty good reason not to use this one.

If you're married, with children, and looking for an alternative to vasectomy, that risk is lower in the sense that should the reverse procedure not go as expected, it would probably be less crushing than the same experience as a newlywed.

How about combining it with freezing some sperm, just in case. Too expensive perhaps?

Freezing sperm costs on the order of $200-400 per year depending on how far you pay in advance. Worth paying if you're getting a vasectomy, but probably not worth it for this kind of (hopefully) temporary BC.

What makes it so expensive?

I think what most people usually miss when dismissing the "condoms fail" argument is that while it's indeed unlikely that condoms literally break if properly used (they're stress tested to ensure a ridiculous level of quality so while possible that's still extremely rare) "user error" is not exactly unlikely. It's also extremely likely that user errors will be reported as condom failures instead.