After struggling with this for a few hours and getting a moderate amount of work done, a buddy recommended a Rotozip, and loaned me his. A quick trip to the hardware store for a diamond blade and I was in business. The Rotozip did the trick. It was fast, went through the grout like my circular saw goes through wood. It also went through the chicken wire that was holding the mortar in place, throwing off some lovely (but harmless) sparks.

Note that I didn't use the carbide grout bit, which I tried and found to be useless. I used a circular diamond blade intended for tile, cement and so forth. Note as well that this blade isn't recommended for the speed of the cheaper Rotozip, but that's what I had and it worked.

Anyway, the combination of the Rotozip RTM01 with RotoZip ZM101 and the Dry Diamond blade worked like a dream. There is a more expensive Rotozip with adjustable speed that should work as well and perhaps be safer.

It Works But It's ... (Rating: 4.00)
Review : This is an easy way to remove a lot of grout and mortar in a short time.... It works as advertised, but I'll mark it down a star for being [to much].

Maybe okay theoretically, but a ripoff in practice (Rating: 1.00)
Review : I've just wasted some money and time discovering the Grout Grabber doesn't work worth a (darn). Apply any pressure whatsoever to the tool, and it bends sideways. Despite a firm graasp on the reciproating saw, this "tool" dances all over the place, thus damaging the surrounding tiles. Bad news!!

I'm going to get a diamond blade for my Rotozip and try that. Meanwhile, we're using a Hilti demolition hammer to tear the whole floor out and start over.

Best Regrouting Option!! (Rating: 4.00)
Review : I have 380 sq ft of ceramic 1'x1' tiles in my kitchen and down the hall, this SIMPLE tool made the job do-able with only chipping (2) tiles.
Don't get me wrong I had some hard grout and it took me 16.5 hrs and 8 double blade (2 blades at a time) changes...I wore those blades down to a nub and they still cut.
If I would had used a circle saw my house would still be in a cloud of dust and I also tried the rotozip thing (my first plunge I was chipping tiles).
I only gave 4 stars because of the dust. It's not dustless but it definalty is less dust.
BUY IT!!

DIFFICULT CHORE SO MUCH EASIER AND FASTER (Rating: 5.00)
Review : Dear John Laurent, I wanted to let you know how satisfied we are with your Grout Grabber, grout removal tool. We are a good size ceramic tile contracting firm and we have to remove and replace tile on a daily basis. Your product has made this difficult chore so much easier and faster. Prior to purchasing the Grout Grabber tile and grout removal was a terribly messy job. customers would complain about the dust created by the old process. Now we remove the grout with the Grout Grabber which causes very minimal dust which makes our installers, as well as our customers very happy. We have been very pleased with the longevity of the blades used to remove the grout and with the Grout Grabber tool as a whole. Thank you for making this great tool!

Well worth the money (Rating: 5.00)
Review : My trusty Sawzall is probably the one small power tool I could not live without, so when I saw the Grout Grabber for the first time, purchasing it was a relatively easy decision. The white grout around a shower in our home had past its prime, and replacing it became the Grout Grabber's first challenge. In less than 2 hours the grout between the 6x6 tiles had been worked down low enough to allow for a new grout application. Wow! Try 2 days or more with a traditional hand tool. The blade action held up well--no noticable ware. I had no trouble reaching all angles and surfaces. The only mistake I made was not buying additional blades when I originally purchased the Grout Grabber--it only comes with one, and unless you have 1/16" grout lines, you'll want at least 2 blades.