A wheel is important, enabling gerbils to get plenty of daily exercise. However, it needs to be a gerbil-friendly variety. A hamster wheel is dangerous for gerbils, as they can trap their tails in its rungs, which is very painful and can lead to swelling and infection.
Stick to a type of wheel created specifically for gerbils.

A gerbil wheel is an important part of the cage, but needs to be gerbil-friendly
Choose a solid wheel, one that your pets can’t get tangled up in. We sell these in the Qute cage and accessories of the Omlet website, but they also come free with any Qute unit.
The wheel needs to be the right size for your gerbils. Too small - and some mouse wheels will indeed be a bit small - and it will not be comfortable to run on. A wheel of seven or eight inches diameter is a good option.
Bali, 6 August 2019
Super looking forewarn to my gerbils