Consensus here looks against, and I believe it really depends on what you're tying. The point of these bobbins is for tension control, which a standard bobbin typically gives, especially for the majority of trout flies.
When integrating in many saltwater and steelhead/salmon patterns, things change a little and the tension bobbins are nice.
Are they worth the money? Like everything else, they are an additional tool to help make tying easier. Lee Wulff never used a vise, and the Dette's (of NY) didn't use bobbins. The answer is a personal one, and depends on your tying.
Brownie gave great feedback in that having just one can be annoying unless it is spooled with the thread most consistently used.
I have a bunch of these, and currently am using the Stonfo Elite bobbins. I have around eight loaded with my most used threads, and love the design. There is only one "leg," which some are opposed to, but it suits my style perfectly (hence my recommendation).
John, if you decide to purchase one, be sure to place a review on here to help others.
TC