Rich K makes a good point,
The slingerland is a very different drum. Mostly because as you say it is COB whereas most supra's (unless you are very lucky to have an early one) arent. but also to do with bearing edges and just being differing drums. maybe this will help your choice:
Sound:
Dark, rich, full sound with texture and cut. range goes from very sensitive to cutting power
Issues:
Unlike the later Supra's they do not usually suffer from pitting because it is chrome over brass. The only issues I have seen are slightly dented shells from the soft brass "pulling" over time and this is usually very easy to put right
Price:
As above, Anywhere between 150 - 250
Summary:
It is no doubt a great drum, im sure it will never have that legendary supra status but for the price it is huge value for money. I havent been able to fault it and it does everything I expect from a brass drum. Opinions will vary as fans of the different drums would have their personal favourites but I dont think anyone would argue this is a really pro drum - a real diamond in the rough.
I love mine - 67' 5" soundking with the twin throw. But if I was given the choice I would take the 6.5" GK which is an absolute lady killer.
IMO - Buy it, Play it, Love it.