Thank you for your question.

Yes, we use Free, Open-source 3 month SSL certificates from Letsencrypt.org. The reason is simple: it is the best and most forward technology at present. You can look at the list of sponsors of LetsEncrypt that put money into developing of this technology- it is tens of IT companies and Google and Cisco among them.
And the result proves to be great!
Compare yourself
https://www.ssllabs.com/ssltest/analyze.html?d=dmpayment.com
gives our domain overall rating "A+"
and look here
https://www.ssllabs.com/ssltest/analyze.html?d=www.facebook.com&s=31.13.77.36&hideResults=on&ignoreMismatch=on
that receives this overall rating only "B". It is 2 levels worse.

Our Free, open-source 3 months ssl certificate is better than facebook certificate. I think, that it is a good reason to trust the acheivement of modern technologies