I’ve only used them once but they do make fmq easier for some designs. And they do help you be a little more confident that you can achieve some designs. Angela Walters has a whole line and videos, but there are a lot of great videos on YouTube.

10 Quilts in isn't very much. You need to cut yourself a break! Free motion quilting is a skill that improves with lots and lots of practice. There is really no other way to improve, except to just keep at it. I will say that I did take a class which helped me tremendously. Is that an option for you? Not an online class, but one with a real live instructor that can give you feedback? Each quilt I make I continue to learn something; not just about patterns & piecing, but also about the quilting process too. Not sure if getting a mid arm in necessarily the solution; It is still FMQ in which you are moving the fabric under the needle. I've been quilting for 7 years now and I feel OK saying that I can do a decent job on FMQ. I am better than some, but not as good as others, but I am usually happy with my quilting in the end. Hang in there and keep practicing. You'll get there:)

I’m in the same boat but have done only a few quilts. One thing that helped me with the length problem was lowering the speed if you have a choice of settings for that. When you do that the speed won’t exceed the setting even if you stomp on the peddle. It saves you from yourself. Start slow until you get better then try increasing the speed.