Never used a Burris posi lock. Im sure it works as they say but Ive never had a problem with a non posi lock. Im a fan of Burris, have several, and recommend them. Same with Leopold scopes, I have some, never had a problem with one, all have been clear, and recommend them, etc. The Burris are a little heavier because of the use of brass in some interanl parts and they are a little less expensive for the most part. I have a Signature Burris 1.5x6x on my 375 that is the brightest, clearest scope Ive ever had. Though there is very little difference between it and the Leopold Vari IIIs. Ive never had a complaint with the fullfields either, either fixed or varibles but there is a slight brightness difference with the Signature series. Best thing to do is look them all over and decide. Best wishes and good hunting.