I have been using Apera for over a year and really like it. Very easy to calibrate. I bought the kit and not even close to running out buffer.

https://www.amazon.com/gp/product/B077Z6LF91/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

I bought this one and it's worked great so far.

pH meter. Something like this. I do not recommend litmus strips or similar pH testers. They rely on color interpretation, and hot sauce contains a lot of pigments which can make that interpretation difficult.

Keep in mind, pH doesn't necessarily mean that botulinum toxin isn't present. As long as you've followed a sound process, you can be all but guaranteed botulism wasn't able to get going. pH readings are primarily used to ensure you've achieved a level low enough to prevent bacteria, including C. botulinum, from thriving once bottled and give you some reassurance especially if you're giving your sauce to someone.