I don't know about anyone else .. but due to my poor vision and I suppose clumsiness .. I've had the most frustrating experience in terms of assembling the the damn needle onto the pen .. I was only able to assemble it properly two out of 10 times .. and now I have a snapped main needle on the injector pen as well as burning through my supply of needles 
!! I personally think that these pens are horribly designed and engineered .. it would be prudent along with common sense to in case the main pen needle in heart plastic and simply exposing a tiny tip; along with a harder tip it would be easier to insert into the secondary disposable needle .. otherwise the user is forced to be very careful and have excellent close up vision not to mention steady hands to accomplish a seemingly innocuous task ..
.. to be continued ...
!! I personally think that these pens are horribly designed and engineered .. it would be prudent along with common sense to in case the main pen needle in heart plastic and simply exposing a tiny tip; along with a harder tip it would be easier to insert into the secondary disposable needle .. otherwise the user is forced to be very careful and have excellent close up vision not to mention steady hands to accomplish a seemingly innocuous task .... to be continued ...