I do have VPS in Vultr.
The connection is good, the price is also good.
$2.50 is for 512MB and IPv6 only. But if you want IPv4 also, then go for the $3.50 package.
Their 1GB RAM same with DO, I guess no need to compare price with DO.
How about their support?
When I opened a ticket, their support is great, but if your ticket is not really high priority, you might need to wait until their support online.
BUT, they do have 24/7 support, sometimes I opened a ticket outside of their online support (wtf, their support hour is from 9PM until 6AM here). They do answer and solve my problem.
Their virtualization customs from your OS. I use Debian, the virtualization from hostnamectl is qemu. While I use Ubuntu, it's openvz and kvm, I forgot which one.
Port 25 blocked, but you can request to open it with open ticket and wanted to open port 25. I got my request accepted. You only need to say how much daily email and for what you want to use it.
Final words:
Vultr's VPS is pretty stable and fast. Their price is the most lowest price I've ever found with Singapore location. I would prefer them for Singapore location if you want to have cheap price with nice support.