Technically, no. The frame build should be of similar quality.

Variances will be the the material and the components.
The Mu Uno is Aluminum Alloy (Dalloy in Dahon parlance).
The Speed Uno is High Tensile Steel. Higher would be Chromoly. Perhaps Dahon upgraded to that in the recent build.

In terms of components: Mu generally has good high end components. Multi-Speed bikes normally have Skewered axles and higher level hubs, sealed bottom brackets and also double wall rims.
Some of these subjects are difficult to parse. Generally Dahon has single wall rims when they offer nutted axles (I would have to study how the Mu Uno was sold). I would prefer double wall rims and the choice of axles. Upgrading BB's are always easy and I do so often.

I have not seen (or taken apart) the latest Speed Uno. The price increased significantly. Perhaps that means that component went up, but it could be that no other market sells the bike so the price is based upon volume. I am not sure.

Mu Uno was always a very nice Bike. Came in a few variations. 20" - full build. 20" Belted. 20" 451 Belted (I think)... I always sold them rather than using them as we have hills, but I thought often about converting a Mu Uno to 3 speed.

Anyway, the Speed Uno is a nice bike and very practical for upkeep. (I liked the old Vitesse D3 which was like a Super Speed Uno).
At present it is the only single speed Dahon. You can get a Multi-Speed IHG Vitesse. Nice frame. Wheels are single rim and nutted axles, but that is the only real drawback to the bike.

Hope this is helpful.,