I also bought 10 grams of pharmaceutical grade Alprazolam from a Chinese API and raw pharmaceutical manufacturer/supplier. They were definately the legit deal, and as soon as I recieved my envelope with the Alprazolam I gave a 1mg sample to a friend of mine who analyzed it for me with GC/MS, and it came out to be 99.999% pure, with the 0.001% of other stuff being solely one impurity, a harmless isomer of Alprazolam, a byproduct of the synthesis of which a minute trace was left in the product.
Regarding dissolving Alprazolam into concentrated solutions, just dropping the crystals in Ethanol and stirring the solution won't really do much, if you really want to dissolve higher concentrations of Alprazolam, you'll have to heat the Ethanol while stirring the solution and then try to dissolve the Alprazolam in it, that way it will dissolve much better, much quicker and much more of it. After the solution has cooled down to room temperature again, the Alprazolam will stay dissolve in the Ethanol and not precipitate. That way you can make a solution of 10-20% concentrated Alprazolam/Ethanol solution mixed with saline solution for injection. There's nothing wrong with shooting the solution you end up with if you do it this way (as long as your Alprazolam is what the supplier says it is:"pharm grade Alprazolam") Temesta and Rivotril also come in ampoules dissolved in the same way, only Dormicum and Valium ampoules are made up differently, Dormicum being dissolve in just water (as it's a water soluble salt) and Valium being dissolved in Propylene Glycol and a bit of Benzyl Alcohol and maybe a little bit of Ethanol too.
Regarding the rush, it really depends on the individual person who they experience it, some think IV Clonazepam or Alprazolam is great, others think it's no different from orally taken. Nearly all benzo's have a very high bioavailabillity though, in the range of 80-100%, so it's not necesarry to IV any benzo's for efficientcy's sake. The only reason Clonazepam, Lorazepam and Diazepam ampoules are made is because they need to be rapidly absorbed by the body and into the brain after administration, in the case of an emergency (status epilepticus for example, as well as other types of seizures) and with Midazolam it's for the same reason, when used as a pre-anesthetic and administered the dose needs to be absorbed by the body quickly to obtain a high plasma peak quickly so the person becomes unconscious quickly, and the other reason is because the dosing can be regulated much more precisely, which is very important when it's used to keep people in a coma when they're in an ICU, to facilitate intubated ventilation.