It's fine as long as used in emergency only. In fact all the new generation cars come with space saver, ie, smaller spare tire. For example ,BMW comes with 135 mm width tyre as donut while 225 mm is stock size.
Just FYI, earth one are made for India tires. I have XM2 on Figo and Earth 1 on Fiesta and honestly I didnt find noticeable difference in grip between two. Have driven earth1 flat out on some twisty wet roads and they held very well.
I apologise for the completely , but can not resit myself.
Do you have Fiesta Classic or New Fiesta ? And is it Diesel or Petrol. Provide any link for your ownership review or upgrades done to your Fiesta, which you might have posted in the Forum. I loved to go through these
You can use it on emergency but still when you can, get a new tyre for spare. A cheapest one will do.
1. Michelin Energy XM2
2. Bridgestone TURANZA AR20
3. Yoko Earth 1