Been burnt before
Had the facebook app aaaaaages ago. Stopped letting me message through it saying that I needed facebook messenger. Installed that alongside facebook app and got maybe 6 hours battery life if I was lucky.
Someone told me that going to mobile facebook in the browser let you send and view messages. Removed both apps and used the website. Battery life massively improved by about 7 hours. No idea what their apps do but they sure won't be back on my phone any time soon.
A strange thing I noticed as well is I keep being prompted to help 'secure my account' on facebook by entering a mobile number. I always close this as I don't want them knowing it. I recently had to install whatsapp to keep in touch with a family member. I gave it access to nothing and typed my brothers number in manually rather than letting it rifle through my address book.
Next time I got the prompt to help 'secure my account' with my mobile number on facebook somehow the site had prepopulated my mobile number. I just assumed it had taken it from my whatsapp sign up, but then I remembered a few weeks later that I used a different phone number to verify the whatsapp account even though it was on another number. Really opened my eyes to the amount of data that they are able to collect about you