I have a 48 Biller, good gun.
The Spearfishing Specialties & Billers are the same guns. The Billers have a hand guard on the grip that I like to use to tie a short line & clip to, for securing the gun when I need my hands free.
SS has some advantages. They have been innovative in certain accessories. Their spare shaft holders are better. They came up with & sell the speed loaders in place of the shock cord, a huge improvement. They have a version called the Commercial, etc.
Also, Kevin is very active on the net, he hangs out on spearboard & freely advises & assists hunters of all skill levels, regardless of what make of gun they use. Biller does not have any such involvement that I'm aware of.
My Biller has gradually been becoming an SS as I make small mods to it here & there
I do like supporting those who support us, and SS has a lot in their favor in this area.
Don't overlook holding out for a good deal on a used gun. That's how I bought my Biller & it saved me a lot of money. People sell guns all the time, usually bc they decided to move to a different gun when their skills or needs change. Keep an eye on the spearboar Member Items forum, good guns show up regularly & if the deal is good, they don't last long. I bought mine there & had the deal closed about 2 hrs after it was posted.