I'm not sure about the "different bonding agent" bit ... The device is demonstrated frequently on QVC by its inventor, I've seen it in Homebase too, where it seems a similar price to that on QVC (taking in account p+p.) Apparently is doesn't 'do' the first course which must be laid to a string line ... for obvious reasons ... but it gives the correct amount of mortar between the bricks _and_ the correct 'indent' -so there's no need to 'point' the bricks. It also does 90deg returns. The inventor claims that it doesn't waste mortar as nothing falls onto the floor and excess mortar can be returned 'clean' onto the board. I haven't used one ... yet ... :(