In-ear monitoring, the professional term is "auditory delayed feedback". This type of headphones in China costs 300 RMB, which is about 40 US dollars when converted into US dollars. The main function of in-ear monitoring is to monitor your own speech pronunciation. Long-term use will make you familiar and immune, so this type of headphones can improve speech, but cannot solve stuttering independently. In 2018, I asked someone to help me design this type of headphones. Because I am an amateur in production, I took a lot of detours and spent 1 year to make it. Now if you ask me to find someone to do it, I can make a brand new one in one month. It took me a year to go the wrong way to design this type of headphones, but it took me three years to explore ways to solve stuttering. So, don't focus on external things to solve stuttering. If you have friends in China, I can sell a few and ask them to send them to you. It's not expensive for a few dozen dollars. Of course, the price you send outside of China is definitely much higher than this.