What are the cons of using an education visa in Thailand?

Most immigration officers will believe that you abuse the visa even if you’re a legit student. Maximum scrutiny

Cons compared to what? Depending on why you got that ED visa, the expectations and rules will be different. For example studying university level diplomas will get you up to a year at a time for extension. Compared to a maximum of 6 months on a language course. There's also a new yearly extension made for those already graduating uni, and looking for work.

Shady language school that you might not even have attended? Different story.

Not sure what visa Andreas was on, but when I got mine I had to get an extension every 90 days, which meant going to immigration with papers from my language school and spending 6-8 hours just waiting and waiting basically the whole day to get a stamp. Immigration officers cane to the school to check that we were in attendance twice during that year, and if you were not in class when they came and didn't have a doctor's note, they could deport you.

Another issue is that if you have an education visa in your immigration history, and try to enter on visa exemption soon after you're done with your classes, you might get denied entry, since the education visas have been abused by thousands of agents selling this visa to people who aren't actually studying. The agents claiming that they can get you a "legit" visa from a Bangkok university are just lying to their clients. A legit education visa is for studying, not just getting a stamp and never actually attending classes.