Basicly all the small blaster are the same, most are of the deadman type. problem with them is that the tip wear out easy, as does the shutoff bar.
Next better unit uses a gate valve that has a 1/4 turn action, problem with this type is they use a Stainless Steel ball and plastic or brass housing. Needless to say the soft plastic or brass gives way under use over time.
The best uses an air operated shut off valve located in toward the tank controled with foot pedal or by hand. Tip threaded to hose. Big $$$$.
Each unit goes up in price but the longer the tip/valve will last. That said the style you speak of in your last paragraph...Deadman type. It comes in a cheap sytle and a more expensive type, difference being a better grade of material used.
Hope this helps and also check out all the YouTube videos on sandblassting.