I have a 10 foot West Marine and its great. Outlasting some of the bigger nsme brands my friends have and it hangs all year uncovered.
I have an 8hp on mine and it does 15 knots with just me, a 9.9 would be perfect, 15hp is probably too much for the feint hearted unless you stay off the throttle...but any RIB is dangerous if you run it wrong as Smitty447 points out.
As for unstable, with a light load all RHIBs float high. Mine floated and ran nice with the recommended max capacity (4 adults, luggage and groceries). But with just one person, especially riding midship for trimming purposes and a nice vee in front, yes of course it seems tippy, but hardly unsafe. Add a person all the way up front with one at the tiller and mine feels as stable even for my usual passenger who has poor eyesight and a lousy balance.
I cant speak for all West Marine dinks, but the single and double floor 3.10 hypalon is a great deal. I like it better than the Defender model and if it continues to weather well, it was a great purchase (tho I did get it on the Summer sale )