Dakno,
I purchased the FG50A bottle here:
http://www.go2marine.com Part # 100086
This is a direct replacement for the original- comes with a bracket but it fits in the original one. The head is a little different than the old one which had a protective wire frame but otherwise identical. It is wired for the engine stop system and has the correct plug. Simple install. $343 out the door and fast shipping.
So, the question isn’t “why did Hunter install these?” Rather, it’s why didn’t all the other major boat manufacturers (beneteau, Catalina , etc), do the same.
The answer is that Hunter spent more money on their boats installing very valuable items which nobody would see at a boat show when considering what boat to buy. An example of this was that Hunter was the last production company to have lead keels. All of their competitors had cast iron years before hunter finally had to discontinue lead to stay cost competitive.
On my 49 a $3500 mains isolation transformer was standard equipment. The Selden in mast furling is a much better system than the ZSpars used by the other builders. It costs more, but it’s worth it.
Yes, having a hole in your engine cover to shoot a fire extinguisher through would work. But, by the time you realized you had a fire to put out, the Seafire system would have done that automatically. I prefer that option.