I'm careful with rear disks, I paid a bit more than £30 recently because I read some review of the specific type of cheap disk on eBay that I was looking at cracking after a short period of time. I ended up buying a JT Braking disk, a brand I trust for sprockets.
Depending on who makes the front disks they might be right and left sided. I have EBC front disks, not the cheapest, but they are well made and these disks' particular design mean they have less bobbins. These EBC disks are also either sided. They've also stayed neat, the bobbins aren't showing any rust, with cheap disks you often see rust very soon on the front floating disks (you don't have this issue on fixed rear disks.) Even though the EBC disks are great I might look to see if JT do disks for the Wee when I buy next, just to save a few pounds. That said, sometimes cheap is false economy and I think when it comes to brake disks this is often true.
I put a cheap Arashi brake disk on the DR-Z, so far so good and they are getting good reviews on the DR-Z forum and some other forums I did searches on. Perhaps they make disks for the Strom?