oceandjinn:
..."is it worth getting as opposed to a decent dive computer"?
No. For recreational diving you will be better served by a decent dive computer.
The reason is precision.
When diving with a computer, the computer 'samples' data (depth, elapsed time, temperature, etc.) according to a periodic interval set by the diver. The computer takes the data and enters it into an algorithm which "quantifies" gas absorption in various tissue groups.
Therefore the computer offers, all else being equal, a reasonably accurate record of both data readings as well as decompression information derived from them.
A Wheel involves estimates - both during the pre-dive planning as well as on the post-dive analysis.
(In fact, any tables - whether PADI, SSI, NAUI, etc. - all involve estimates of both depth and elapsed time during multi-level diving. This is why tables can be problematic if your dives are not square profile dives.)
The Wheel is intended to allow the planning and analysis of "multi-level" diving, however, in terms of measuring how long you were at depth X and then afterwards at depth Y, obviously the Wheel relies on your estimates. Your estimates may be close, but even under the best of circumstances your estimates will not be as accurate as the data sampling performed by the computer. Then if something happens to distract your concentration, your estimates may also be wildly off base.
Considering that the computer also tracks Surface Interval duration, so that multi-level diving is performed with a cumulatively more accurate measurement of total residual nitrogen (which can also be over several days in a row, not merely several dives in one day), and you can see clearly that for most recreational diving situations a decent dive computer will be a much safer alternative than a Wheel.
FWIW. YMMV.