What size needles did you get--many of us use 31 gauge with 1/2 unit markings. I can put all the info if you need it. You may have to special order thesyringes with 1/2 units but def. need those...you may find that you do DOWN in dose too,my cat is on 1/4 unit.which is teeny.you could not figure that out with a 1unit markings needle.
I've used both the pens,vials and cartridges. I like the pens the best because they have the cover, so in theory are safer if you drop it. I've broken a vial before and then you don't have a backup.With both the pens and the cartridges you have backups since they are smaller portions, which is nice.