I don't understand why anyone would bother to make one for scanner use as its an offshoot of a much larger HF amateur antenna that is used horizontally where you can live with the lobes easier.
Good evaluation of the antenna. And taken by itself, it doesn't seem to make any sense. It's one reason you never see any of these on a hilltop.
But from a consumer scanner-front end standpoint (generally poor, especially if using a handheld), prone to overload and desense, in high signal areas, the non-ideal lobes provide a certain amount of attenuation on their own above VHF which may cut down on having to use programmable attenuators.
Back in the day when this was conceived, with the pro-2006 front-end being the standout exception, yet STILL, this provided much better reception than the included whip screwed into the top. It helped lesser scanners, especially those without programmable attenuators, mainly for 800mhz overload, even more.
So from a *consumer systems standpoint*, the reasons to build one might be:
1) Far better than a back-of-set antenna.
2) Indoor versions can use wires attached to the transformer instead of tubing.
3) Low parts-count, quick build time, and non-critical project assembly.
4) The bang-per-buck is high - despite the antenna not being purely ideal on it's own.
5) Takes up minimal space in the garbage can if one is not happy with it.
But don't put makeup on a pig. Only take it so far, which is generally a quickie non-optimal installation to a receiver or handheld with a poor front end.
For those starting to DIY, it can be a confidence-building first stepping stone to something more specific and higher in performance.