I've only just heard of this, and, as my Meccano set (with some bits dating back to 1910) is getting all bent and rusty, does anyone have experience of this as a prototyping tool?
I did dally with Lego***** some years ago but felt restricted by the dimensional limitations in that everything has to be built up from the bottom and you couldn't shoot off at any angle as you could with Meccano.
ISTR also some years ago a competitor to Meccano as Fischer Technik?
***** Invented by the Brit Hilary Fisher of Kiddiecraft, and design stolen by Lego, who later on purchased the rights to the design from Fisher's widow in order to sanitise what they were doing, but it still hasn't stopped their claiming that they invented it!