Look at warranty
Look at power use, wattage
Look to see if it has battery backup option, support and what is needed to setup
Check to see if it is supported by your controller, if one is used, or planned
If going with Gyres make sure you understand how forward, reverse, work and setup accordingly
Add in 1 spare for easier cleaning, maintenance, and emergency backup
Above all, set a budget and consider all above before making purchase. Flow is one vital role in our systems and it will change the longer you stay in the hobby. Flow with a new system will be different with a successful one at year one, two, three, five, and ten.
Plan accordingly.