Pros: cheap, sterile, convenient, comfortable to give and to get, versatile
I'm totally NOT into needles, but when you have allergies bad enough that you ASK for allergy shots when you're a kid, that's bad allergies. I am allergic to all animals, all plants, and all molds/mildews. Luckily, I haven't had any major food reactions (yet). But from my early teens until last summer, I took 1 or 2 allergy shots a week. My mom gave them to me until I went to college, and then I gave them to myself.
These are the syringes we always used. I've gone through literally hundreds of these. As far as needles go, they are pretty comfortable. If you don't tense up, and you don't look at it coming, you almost can't feel it (until the plastic top of the syringe touches you and you know the needle is in you).
I had little pre-made vials of allergy medicine to inject, so I didn't have to measure exact amounts of medicine, but if I needed to it would have been easy---the one cc has 100 divisions marked, so you can clearly measure 1/100th of a cubic centimeter (that is pretty small!!!).
The box of 100 syringes opens up to reveal 10 sealed bags of 10 syringes each. It is easy to keep track of which syringes are used. Even though they don't get dirty, both ends of the syringe have caps. To use a syringe, you take the cap off of the plunger end and hear a pop as the seal breaks. Then you take the cap off of the needle end. After use, you cover the needle back up (if you don't have a way to clip the needle off or a biohazard "sharps" container), but you don't (can't) cover the plunger end. So if you accidentally threw a used syringe back in with your new syringes, the fact that the plunger wasn't covered should tip you off that it isn't sterile.
When you take the cap off of the needle, be sure and pull it straight off--sometimes the needle bends easily if you pull the cap off hard and aren't perfectly straight off with it (and you don't want to inject yourself with a bent needle, trust me). Also, if you re-cap the needle, be straight back on with it and be careful. More than once my mom or I have gone in at an angle and been poked by the needle when it came through the plastic (ouch).
These syringes provide a comfortable injection for allergy shots. They are short enough for small hands (I'm petite) to steady the syringe and operate the plunger smoothly with one hand (roughly 4.5" long). They are narrow (about 1/4" in diameter) and not imposing and scary-looking (if you have to give kids allergy shots, this is important).
These syringes also come in handy for other times when you need a sterile needle, such as getting splinters out, lancing boils (sorry to be graphic, but some people may find that useful to know), etc. To sterilize a pin for such uses, you would have to heat it until it was orange, and then guess when it was cool enough to touch the person (or yourself). If you used any other method to test to see if it was cool enough, or ran it under water, it would contaminate the pin again. Or you could pour alcohol on a pin, but that would burn when you put it in a wound. So having sterile needles on hand is a great convenience.
I don't remember having to have a prescription to get these, and I got them at Walmart for a little over $35 without a copay or anything, so for about 30 cents each, they are money well spent. I stopped taking allergy shots last summer when I suddenly had a reaction (went into anaphylactic shock) after an allergy shot, even after 20 years of them. My doctor pulled me off of them. So I still have a lot of these syringes around, but they are so handy I won't be getting rid of them. I'm sure with a 6 year old I'll be using them for splinters and things like that for years to come.