I feal these are a much better option. Something like the 3ml BD with a 1/2in or 3/4in removable needles for gauges larger than 27, and inch or 3/4in for gauges less. if you go with a long small needle its almost impossible to pull the blood through to register, so a 26 gauge with an 1.5 inch will "work" like crap) You can get the needles in what ever gauge you want or use. They are made much better than those cheap ass flimsy insulin rigs. Insulin rigs are designed to just poke through the skin and deliver a dose subcutaneously. They are not designed to hit veins. The needles are often shit. The syringe is usually made as cheep as they can make it.
With the removable needle if it gets clogged you can just unscrew it off and load a fresh one. If it totally fails you just pop the needle off and plug it (obviously don't reuse that syringe for an injection).
People who use the insulin syringes just seem to miss and miss after a while, then because of the needle length they can register and blow out easier, get bent, etc. Then the syringe fills with blood and this coagulates to plug the needle.
With a stronger and longer needle its much easier to hit and hit well. The gauge of the needle is the same as what is on the insulin syringes so the damage of a single shot and resultant track is the same. But since they work better people do not find themselves doing nearly as many attempts or misses as when done right they register very well and are farther in the vessel.
People like the idea of the insulin syringes as they want the least amount of damage. And they work great for small veins that are close to the surface, like in the hand. But for others they often work so crappy that we end up looking like pin cushions and damaging ourselves way more. They also have that tendency to register and then miss; this means that we are then bleeding out in all those spots which causes the bruising. Every Time we are forced to try again then we put another needle through the skin and this increases chances of negative outcomes and leads to more noticeable damage like track marks. The more we hit, scrape, poke through a vein the more damage is done, the more scar tissue forms, and the greater the chance of the vein collapsing.