I never really noticed much change,but i never really let it get a real long steep,as i only made 30ml at a time and went through that in a week,although when i started trying other flavors,i did let a half bottle of red sit for about 2 weeks,and while there was a very slight change,it wasn't enough of a change to make it worth the wait.
Your not alone,i have read from several people that say m-type is really good,but it was definitely not my thing haha.Oh,and i never even went close to 5%,my mix was at 2% and it was way to strong.I just recently traded off the remaining flavoring i had from it,and like you,the guy i traded with said it was really good after he made some up.I thought about trying it again at a lower %,but i just couldn't bring myself to it,after trying it fresh and roughly 6 months steeped,my brain just wouldn't let me attempt it again haha.