Mom regularly broke them in half for the Laundromat and liked the cleaning results, but then all of the detergents said to use half as much in a front loader and our clothing was not that dirty. There were free samples in the mail and coupons inside the samples, in the paper and in magazines plus the tablets were on sale all of the time in the stores so they were heavily marketed. I guess that P&G & Lever Bros. knew there were still a lot of front loader washers and combos in the early to mid 60s so the tablets had low sudsing formulas which probably helped sales. I wonder if detergent manufacturers consulted with washer makers about whether new detergents would be high, controlled or low sudsing.
Thanks for the answers about the liquid detergents and temperatures. The European liquids must be better behaved at high temps than liquids in the US.