the big problem with those is they have very bad flight times, they burn a ton of fuel, the engines are very expensive, and the engines aren’t reliable for practical use.
To put the fuel consumption in perspective running two Nike engines from AMT you will burn upwards of 1 gallon per minute which will give you about 5 minutes of flight time with the US legal limit of 5 gallons(assuming you can keep the top speed under 55 knots so it can qualify as an ultralight). Even with a thrust augmentation device that can increase thrust by 100%, you could only get about 10 minutes of flight with 5 gallons of kerosene.
As cost goes a single Nike engine from AMT is over $25,000 and you need at least 2… Also the turbines in this size range will typically need a rebuild every 25-75 hours which gets really expensive.
The final and possibly biggest challenge is the reliability. Unlike Paramotors, if your engine fails you will fall like a rock out of the sky. And to make it worse you have 2 engines on each side that aren’t known for their reliability and if either of them fails you could die.
It would be really cool someday but I don’t think our technology is there yet.