This is just my experience with things over the past 2 years. I am currently only like metal devices, but you just need to make sure you have something "solid" that isn't going to wiggle around. The most important measurement though is the "ball gap" the distance between the ring and the cage. This is where 1mm can make a big difference. I personally wear a smaller cage length due to "fashion" and I don't want a noticeable bulge... I think it is "ok" to have a short length as long as it is compensated by a wider cage giving you a little more room to squeeze into. The last thing you want is discomfort that causes you to stop wearing for a couple weeks to due a skin issue. Best luck.