In reply to Gaston Rubberpants:
It was originally sold as auto-locking which in reality (barring something wierd) it is. However the regrettable habit of climbers to override the auto-locking made it nescessary to change the instructions and tell climbers to keep hold of the dead rope which meant the device would lock no matter what was done. The ghastly term `locking assist´ was born which if you ever do a drop test is clearly a misnomer since the belayer in fact does nothing whatsoever.
This has also occured with the Trango Cinch where originally one was instructed to effectively throw the device away from you, in other words use it as auto-locking, however climbers insisted on still pinching the body preventing it from re-orientating and locking. The newest instructions now tell you to install it differently so that is effectively in the locked position all the time. Not of course that Trango has seen fit to contact all the purchasers to tell them nor widely publicise the fact but since that would be a tacit admission that the old way was incorrect with all its potential its liability issues.
The GriGri was originally devised as a lead rope solo device (and is still sold for this by Rock Exotica) and is certainly the most popular device in use for this, it was subsequently modified by Petzl specifically as a auto-locking device. There are some who prefer the Eddy which is harder to manually disable the auto-locking (so probably better for the OP´s belayer) but the lowering is the pits in comparison and rope diameter/feed more sensitive as well as expensive and heavy.
The draft UIAA standard for locking-assisted belay devices includes a hands-free (auto-locking)drop test onto the device which currently it is thought only the GriGri and its clones will pass. Including this test may well prove controversial.
The Smart is, of it´s type (assisted braking) probably the best available at the moment in my opinion (sorry Click-Up fans) but certainly isn´t a GriGri replacement for me and many users since it does none of the things I want or need well enough. If it suits your needs then probably a good choice but for the OP´s belayer potentially even more of a disaster.