I think that the major benefit of SSDR is in the freedom to make/design/modify/improve/test without the requirement to seek engineering approval from any regulatory body. From this position it would seem that the target market would be the home builder experimenter types.
Many of the designs which are likely to meet the SSDR basic specification will be the American part 103 ultralights which I believe are all plans built or kit built designs. The remaining types are generally flexwings which just happen to fall within the SSDR spec. The SSDR spec has been carefully created to ensure that the performance of anything that meets the requirements will be quite modest. Many second hand LAA type aircraft will cost less and outperform most SSDR compliant designs.
Why would you want to buy an SSDR type unless you wanted to be free to tinker with it? If you were likely to tinker with it, would you not want to start by building it?
Rans6