According to Walter Martin, Mantey carried the KIT with him as he traveled. This brings up a question. Why would a scholar of his caliber bother to take the WT KIT with him if it was so badly translated? Me thinks, he found a lot of good in it which he did not want to admit publicly. If that wasn't the case, and his motive was to criticise it at every oportunity he got, it would show that Mantey was emotionally obsessed in proving the WT wrong, which would indicate he wasn't much different from WT and Evangelical fanatics.
I can think of a couple of reasons why Mantey might have done that (if, indeed, he did - I'd be interested in seeing the quotation from Dr. Martin).
First, it may have been something about which he was confronted frequently, therefore felt he should have the book with him in case it came up.
Second (and more likely, imho), the KIT contained a perfectly good reproduction of the Westcott and Hort critical text of the NT. The Watchtower had nothing to do with producing that Greek text; they simply lifted it in toto as the "original Greek" in the KIT. If I recall correctly, the KIT sold for $2.00 when it was first issued - probably a whole lot cheaper (and hence more replaceable, if something happened to it while traveling) than other critical text editions available at the time. The only part of the KIT that was actually the work of the WTS was the NWT rendering in the margins. The interlinear English renderings were probably simply taken from various lexicons. So the KIT could have just been an inexpensive means of carrying the W&H Greek text while traveling.