To start I will concede that the software is very effective at modifying AI written content to avoid AI detection. Their advertising makes it very clear that is their focus and it does that well. Unfortunately, gibberish or incoherent writing won't help you rank OR keep people on your site. In the real world, quality is at least as important as AI detection and while right now there is still no or little penalty for AI writing, quality is probably more important.
To be clear, I gave StealthGPT a sincere try by regenerating with all the different modes and tones available attempting to find one that was acceptable. In total, I tried more than half a dozen combinations and processed more than 10,000 words through these attempts. Unfortunately ALL the StealthGPT outputs were useless for a professional business site. Some were okay but not very professional. Many were pure nonsense. At this point StealthGPT output is unacceptable.