Interesting reading all of the comments
For the majority of our clients they will just be used in exactly the same way as our jets always have been and with no need of any of the benefits. A jet is a jet and it will perform much the same as the old ones.
The benefits for users as we see them:
1. Jets can be swapped over quickly - clients have already commented on how useful this is and has allowed them to try out jets they have not used before.
2. Uses John Guest connections which are easier to fit then the barbs on the fanjets - this allows for easy dismantling in case of jet blockages etc.
3. Fanjets are more robust due to the lack of extending barb shaft on the back of the brush
4. Fanjet versions are now flush to the brush on the bristle side, thereby reducing the possibility of catching on window bars
As mufcglen mentioned though you cannot have two jets next to each other as with the older style. However it does only take seconds to switch out the new style jets or as Spruce has said you can drill a 4.8mm hole in the brush stock and fit a pair of the original pencil jets if this is still needed.