I'd go with the 26" auto-lock. The 21" is to short to use for blocking. Your hand get to close and your elbows end up stricking out to far. Plus when stricking the more distance the better.
Auto-lock is good because you don't always have a good place to retract the baton. Also when you testify in court over stricking someone with a steal instrument. They may ask you to demostrate expanding and retracting the baton. It looks like a violent weapon when you must leave the witness stand to smack it on the floor to close it. And luck being as it is, you'll have to smack it a few time to get it to close.
I have the **AUTO LOCK** 26inch it's better than the 21. The 21inch is much to small. I have also added the **HINDI CAP** to the end of my baton. It works great and other people in my dept. have looked into getting it.
i carry a 16" on my patrol belt; i have 2- 3 mag pouches but i only carry 5 mags and use the 6th slot to carry my asp. i got the 16" asp because i don't feel the need to make up 4 anything! Just Kidding! No, i carry a few knifes lots of ammo, a primary weapon a secondary weapon a 16" suits me well.
We also do cover a few mission areas that we are in civi's and carry side arms or nothing at all. So a 16' asp, a surefire defender and an emerson kramabit works good in civi's.
26 inch ASP......I have actually had to return it to the ASP factory because the damn thing wouldn't retract. They sent it back and said that they fixed it and refurbished it as well. The thing looked brand new and they did it free of charge although I still have to smack it on the ground several times to get it to collapse.
I initially had the 21" Autolock. I liked it because you could silently deploy it and collapse it. However, I found that it did not always positively lock when rapidly deployed as opposed to passively deploying it. I did not like the size, because the blocking issues already addressed above. I also found that applying control holds and techniques on large subjects was difficult with a short baton. I traded the 21" Autolock in for a 31" ASP. Great baton, added reach, a bit cumbersome. I also felt like I was carrying a baseball bat around. I decided to go for the 26" and opted for a Monadnock straight baton. Optimal size. Practice with a few different sizes and compositions until you find one you are comfortable with. After all, you are the one that may need to rely on it some time, not any of us.