longvl85,
Yes, the MiVO-250 is capable of supporting POTS lines, T-1/E-1/PRI, and SIP for trunking purposes. Going with a refurb system is a crap shoot, but as long as the vendor is able to support it with updates and software assurance then all is good.
What you want to know about the controller.
1. Is it an HX or CS controller? By default the CS has native support for 2 POTS lines and 2 Analog/Single Line Ports and the HX has native support for 4 POTS lines and 4 Analog/Single Line Ports. The HX controller is the latest controller and the CS controller is no longer supported by Mitel. There are other differences but most likely those will not effect your decision.
2. What software version are they installing it at? The latest version is 6.3 which just came out at the end of Feburary 2018.
3. Is the vendor capable of supporting the refurbished product? Some resellers are not able to support older equipment and do not have support from the manufacturer.
You could have your local vendor sell and install the system at the remote location instead of going to a vendor you may or may not know that well. It is usually best to have the same vendor supporting all of your systems; most Mitel vendors tend to work well with other Mitel vendors for remote support.
Thanks,
TE