I used another VPN-service for free before with no hassle at all. But there was the time to get a complete VPN-service to be covered 24/7.
I chose SURFSHARK, because they offered a fair price and had a quite good rating at various websites. After installing SURFSHARK VPN on my computer I could not connect to various email servers via Thunderbird anymore:
The email servers sent a popup message that the (now new) VPN is being blacklisted.
Unfortunately SURFSHARK´s support service could not advice me to solve the problem, so I had to cancel their service within the 30-day-trial period.
SURFSHARK tried hard to keep me as a customer, but when I repeatedly told their customer service that I want to quit, if they don´t solve my problems with receiving AND sending emails - and they couldn´t - they finally let me go.
They promised to fully refund my money within 10 days. If they -again - fail with that, I will keep you updated.
For me it appears that SURFSHARK cannot handle yet all problems coming along with a VPN service - I wish them all the best to solve their problems quite soon!