Did you know there are only three basic low end ribbon mics? Any differences within these mic types between manufacturers come down to quality control (ribbon sizing, installation accuracy and tension), component details (wire used, transformer type, connectors, headbasket design) and aesthetics. Here are the three "families" of inexpensive ribbon mics...
1.) Short ribbon with wide magnets (ex: Cascade Fathead and Gomez Michael Joly Edition, Nady RSM-4 & RSM-5 etc.),
2.) Long ribbon with narrow magnets (Apex 205, Nady RSM-2, ShinyBox 46, Cascade Vin-Jet etc.) and
3.) Dual ribbon (CAD Trion 7000, Avant CR14).
A full rundown of the various attributes of these ribbon motor types can be
found in this thread. But to summarize:
1.) Short ribbon with wide magnets - has an early HF roll-off making it ideal for taming guitar cabs, screechy vocalists, cymbals and horns.
2.) Long ribbon w narrow magnets - has the most extended HF response of the three "Chinese" ribbon mic types. A more "Hi-Fi" sound not as dark as above.
3.) Dual Ribbon - increased sensitivity over the other two types, a bit "thicker" bottom end due to the dual resonant ribbon frequencies (which are never exactly the same), but suffers from off-axis phase cancelation coloration due to source-to-ribbon arrival time differences between ribbons.
Can you tension a ribbon yourself? Sure. Buy two mics, learn on the first, when you break the ribbon you will have learned something about ribbon mics than can only be gained by actually handling them - then apply it to the second mic.