I almost always used the auto-injector. I like how you can set it to the exact depth instead of eye balling it. If you used trimix much you probably accidentally injected into the lining instead of the spongy sweet spot at some point which can leave a nasty welt. You can still do that with the auto-injector too but I feel it’s less likely.

Also the auto-injector is a good option if you’re on a date and you’ve been drinking. lol