I recently purchased two of your Infin8 halters in a size 3 and 4 for our 10 month old Eng Staffy x Bull Arab and our 16 month AmStaff x Dane and I have to say it is honestly the best buy I have made regarding the dogs besides actually adopting them. Our AmStaff is a big boy weighing in at 40kgs+ and stands hip height on me (I'm 5'10), being forfeited to a shelter at 7 months old because he was too hard for his old "owners" to control, he didn't have much in the way of training or doggy etiquette, is very cautious when it comes to meeting new people and animals, and still gets understandably excitable whenever he is taken for a walk (which is daily). As much as my partner and I love our pups to pieces, coming home after a long day of working we were starting to dread having to take the dogs for walk and recently with my partner starting study again he was not getting home from work until midnight on week nights, leaving it up to me to walk our boy and girl by myself. As I previously mentioned, I myself am a 5'10, 60kg, 20-something in good physical shape but combining the 40kg pulling ability of our boy and the 25kg ball of energy and extremely friendly little girl who loves to greet everyone was so overwhelming for me that I was getting home from work and mentally preparing myself to be dragged around the oval by my pups and praying there was no dogs unleashed who would come speeding up to play with our girl leaving me to deal with our boy's protective caution over myself and his sister. I was desperate to find something that would make walking our pups easier on not only myself, but on them too and stumbled across this site via a link on "The Yellow Dog Project"'s facebook page and after reading a testimonial of another AmStaff owner I decided to purchase the halters. It only took three days for the halters to arrive and as soon as I got home I ripped them out of the packaging, read the instructions, hooked the pups up and was out the front gate, instantly amazed at the difference and they'd only been wearing them for 2 minutes! At first my boy was not impressed at all about having this thing restricting his pulling but quickly got over it when he realised that it wasn't coming off and he wasn't going anywhere until he stopped trying to rub it off on the ground. The first walk saw the lady who always has trouble controlling her Kelpie x Heeler on a retractable lead growling and eventually trying to lunge at my pups and myself while we were taking a rest on the bench when she finally made her dog walk (dragged) past, this normally would have my boy lunging right back trying to pull me with him and my girl hackles raised and growling trying to stand in front of both myself and our boy. Instead what I saw was my boy and girl both sit slightly in front of me, no yanking or pulling, staring at the other dog until her owner managed to drag her away with the tiniest warning growl I have ever heard come from either of my pups (this not-so-friendly dog is the only dog in our area that my boy and girl have a problem with) and myself still sitting on the bench with the leashes completely loose soon covered in doggy kisses to make sure I was okay. After three nights they were both 100% used to walking with the halters and sitting quickly for me to attach it to them as soon as I pulled them out of the cupboard. When my partner was finally able to join us for a walk after maybe a week of walking the pups with the halters he was so happy he actually did a little dance around the oval while laughing like a maniac, his smile lasting for the rest of night as the dogs passed out early on their bed sleeping all the way through the night 'til late the next morning. I now get excited about walking our pups and often go for twice as long as I normally would, which the pups are always extremely happy about. If you are having any doubts about this product then don't. If you have a serious puller, I urge you to purchase one of these and be stunned at the difference it makes to your pups and yourself. 100% the best thing I've ever done to make my dogs lives easier. Sincerely, An extremely happy big dog owner and her extremely happy pups. (ED Note) Infin8 Halters were redesigned by Black Dog in 2016, the new version is now called Haltermate.