I do not think the Loctite product is an Ambroid clone.
The base of the Loctite product is polyurethane, not cellulose acetate or cellulose nitrate. See:
http://henkelconsumerinfo.com/produ...S&LANG=EN&COUNTRY=US&VKORG=3450&MATNR=1360694
Further, as far as I know, the solvents used in Ambroid were acetone and alcohol (similar to today's Duco cement). These solvents are much less harmful than MEK. I do not believed that Ambroid contained MEK.
Methyl ethyl ketone, used in the Loctite product, is a nasty chemical, a known carcinogen, suspected of causing birth defects, and otherwise hazardous. Used in small amounts in a very well ventilated area or with an appropriate respirator mask, the Loctite product's potential for actual harm is likely small, but it is not non-existent. The fumes should not be breathed.
See the MSDS for the Loctite product:
http://henkelconsumerinfo.com/produ...S&LANG=EN&COUNTRY=US&VKORG=3450&MATNR=1360694
The MSDS for Duco:
http://www.onboces.org/safety/msds/D/Devcon Duco Cement August 2002.pdf
I have never used the Loctite product, so I have no idea if it performs well -- I suspect it does, because Loctite products generally perform well.
But when other less noxious glues (or even varnish) can be used for a traditional canvas on canvas repair, and duct tape can be used for a very effective temporary repair, I see no reason to mess around with something containing even small amounts of MEK.