Adding a suspension seatpost to a folding bike can be tricky, as folding bikes tend to have very long seatposts.
The seatpost on your Dash is 450mm long. The Thudbuster is offered in a 420mm length on the LT model, not accounting for the 'sag' that will occur when you sit down. If you've still got at least a couple of inches that you could raise the seatpost, it will probably work for you.
Your stock seatpost has a diameter of 31.8mm and the seat tube is 34.9mm. It uses a shim to reduce the seat tube to match the seatpost. The Thudbuster is not offered in 31.8mm, but it is offered in 31.6mm and you can swap the shim to match it.
Be sure to select the 31.6mm size and you will need to get the shim from Cane Creek directly or your local bike shop, or any number of other online sources.
I hope this helps, feel free to reach out if I can assist with anything else.