Sharpmaker with adjustable angle? Doing so defeats the purpose of the design. Sharpmaker is still freehanding with a help (similar to some Japanese artisan that tilt the stone).
For human to hold a consistent angle requires training. The sharpmaker is designed to help in this, so a 10 degree difference set there is to provide most utilitarian edge. If it's made to narrower angle range (increment of 5 inclusive), it is doubtful average human with minimum training can take advantage on. So if the need to have exact angle is there, guided system is the way to go.
Totally agree with David (OWE) on the learning and practicing, and with Omar on what's best is what's one finds adequate for the need. One can simply want to have a working edge, or pursuing the ultimate edge that split atoms

. Both are valid as choices we each make.
Lastly, I guess Mag quoted Jason that 'you are the best sharpener', which include what David, Omar and many others here said. YMMV and what makes you happy.