There were considerable posts on the MDS engines in the day, most were pretty unkind in their remarks about the engine. Many were about the carbs and there were quite a few carbs that were substandard and many did not put the base o ring down and only used the body ring which did not give an effective seal.
The most damaging though was the R/C addiction to 15% nitro in an engine that really did not use more then 5% and did better on FAI fuel. Without adding a few head shims you literally beat the engine to death, the continuous overheating with cheap fuel with little oil didn't help either.
Suprisingly it also was an engine that did benefit from some running in before you slapped it on your model and left it to self distruct.
With these defects it was no suprise that the engine line got panned. I had seen heli engines throw the rod in 1-2 runs simply because of 30% nitro and no run in or reading the instructions.
The problems were eventually too much for Horizon and they dropped the line and created the Evolution line.
In defense of the MDS it wasn't all bad but it required some common sense to get them up and running properly. Given the prevailing mentality of many in the R/C game that made it a doomed project from the start.