I've been very pleased with the technique. You've read this thread, right?
Poor man's surefire perfect beam
I've been using this technique recently on various Pelican bulbs up to the 3854-L, often on only the lower half, masking the top half of the bulb with masking tape. No bad experiences so far, although I suit up quite a bit before doing it (safety glasses, face shield, latex gloves inside leather gloves, lab coat) - I've been trained in chemical handling and have a
lot of respect for the HF (hydrofluoric acid) in that chemical etching paste. 5 minutes of application time is plenty. Let the bulbs dry off for at least a day in a warm spot to make sure all moisture has gotten out of any potting compound.
BTW I've found that there is usually a considerable improvement in beam quality, but IMO beamshots make the improvement appear to be greater than it actually is since the brightness in the hotspot tends to oversaturate the camera for that region. While the hotspot doesn't become perfectly uniform 'inside', the
shape of the hotspot does become considerably more circular. YMMV of course.