Do not be impressed with a low price on any shop machine. Initial price is a small part of the eventual total cost of owning and operating it.
If a cheaper underpinner is inconvenient to use, or if it has limitations such as moulding size or profile or hardness of wood, or if extra time is need to set up, or if you have to re-do miters once in a while, the dollars saved are used up in a short time -- and the deficiencies go on costing you for as long as you have the machine. And once you buy it, you will probably learn to tolerate it; you'll be "tweaking" it, manipulating it, and finding ways to make it work until you can't stand it any longer. Then you'll buy the machine you should have bought in the first place.
My advice is to investigate all of the machines on the market, look for value and buy the machine that best fits your needs for at least the next five years. If initial cost is an issue, delay buying until you can pay the price of the most suitable machine.
Manual v-nailers are OK when time and convenience are not issues, such as for hobbyists, photographers and artists who will use it only occasionally.
For any production situation, a pneumatic machine's extra cost will be recovered in a short time with convenience and savings of time. The more sophisticated the machine, the more speed, accuracy, and convenience you will enjoy. Whether that is worth the extra money is a decision for you to make.
What is your time worth?