Yes indeed, Rushton built some fine boats in his time. He was quite the salesman too...!
While Rushton held patents on some sailing canoe hardware, the Radix centerboard was not his. That was invented (a descendant of a variety of folding boards) by the Messrs. Root and Childs of Brooklyn, NY. It is a clever device, though performanc-wise inferior to a solid-plate centerboard. It's main reason for popularity was that it folded into a 4-inch (including keel and keelson) trunk, which put all but the handle below the floorboards of the canoe and left plenty of room for sleeping.
Rushton designed the Indian Girl in 1901, and it went into production by 1902. He really had no interest in the rag boats, so hired down the Roundy's from Bangor. They may have worked for Morris, which would explain the similarities between IG and Morris canoe construction.
The all-wood canoes were a different story, and Rushton touted their superiority over canvas canoes right up until he died in 1905. The Ugo and Igo are very similar, but if you compare their hull shapes (which can be found in one of the catalogs published 1896 and later), you can see they are indeed quite different. The Arkansaw Traveler is also a member of this family of canoes. The Nomad, a decked sailing canoe, is built on the hull of a Ugo.
A fair number of these canoes survive. Apart from a number I know of in private collections, there are several in the collections of the Antique Boat Museum in Clayton, NY, the Adirondack Museum in Blue Mountain Lake, NY, and Mystic Seaport Museum in Mystic, CT. Perhaps you should make a summer-time pilgrimage - it would be easy to hit the Assembly, the ABM and ADKMus in one trip...
There is no really good way to determine how many may have been built. The three models (IGO, UGO and AT) were designed by Benjamin Kip, in time I believe to be exhibited at the Columbian Exposition in 1893. They continued to be offered until the factory closed in 1915, though probably in quite small numbers after he died.
I could go on for days, but you've probably got better ways to waste your time...
Cheers,
Dan