In a way, yes. However, I have noticed instances where kick shields used to drill roundhouse kicks turn a so-so martial artist into a CRAP martial artist. Not that the kick was any less fast or any less powerful.
The problem is that the kick shield is held outside the visual frame of the body. So the poor student is kicking at an area not central to the objective -- that is to kick onto the human body. All the training aid was good for was to drill a powerful kick on a flat pad held 30 cm away from the body. Why do you think success would falter? Both the eyes and the weapon are calibrated off the main target!
It is up to the instructor to mix and match the use of training aids and kicking onto the body proper (with guard up and guard down) -- this in turn will help students learn how to fully maximise the versatility of taekwondo's kicks.
To think that all kicks are only successful at full extension and maximal range is to cheat yourself of the real tactical advantage of developing accurate and pragmatic kicks.
Related topic on the use of kick shields and muscle dynamics ...
Won-hyo: Where are your eyes on the back of your arse?
And of course, check out the training equipment at the Traditional Taekwondo Shop.