You asked for it, you got it:
The x number of small non-certified engines will not add redundancy, they are in fact very noisy, and terribly uneconomical (as a reply to your comment).
The good old piston engine is extremely reliable compared to these mini jets. Certified GA pisyon engines are tried and tested, and you can bet your mamas behind that they will function properly the whole service interval. The mini (or micro) jets, not so much...
The mini jets are stupid loud. It is incredible how much noise they make compared to their size. Having multiple of those sitting in front of you screaming like nothing you could ever imagine, well... I think they actually are the most efficient way to convert fuel into noise. Which brings us to:
They will also be disappointingly unefficient (other than producing noise). As Robert already commented in his answer, they would be operating in a suboptimal speedrange. Sure, they are used in hoverboards and other doohickeys that are even slower than a C-152, but the reason they are used in such applications is their size and relative safety compared to piston engines with large propellers.
All that (and Roberts excellent answer) being said, if I had the time, I would certainly build what you have proposed in your question. Just for shits and giggles 😃