The halo is small, unobtrusive and nearly omnidirectional with a gain approaching 0dBd apart from one deep null, over a narrow part of the polar pattern. I have used one on and off for several years and have managed to work some useful DX on SSB and CW with one mounted on a pole at the side of the house fed with RG58 coax, which is rather lossy at 2m.
The choices appear to be:
The turnstile uses a pair of phased dipoles mounted 90 degrees apart. These have slightly more gain than a halo and a more uniform polar plot. They are larger though, although visibly acceptable.
The big wheel, also known as a clover leaf because of its shape, consists of 3 full wave loops fed in parallel. Although bigger than the previous 2 omnidirectional
So, when I move to my new QTH later this year, I plan to install a couple of 2m big wheel antennas on a pole clearing the roof top. Fed with better coax, and being on top of a small East Anglian "hill" (rather a contradiction) it should be a useful antenna to work the occasional contest and hunt some DX in an opening.
Big wheel antennas are available commercially from Wimo in Germany, together with a suitable phasing harness. Alternatively, they can be fabricated from aluminium rod and an assortment of hardware parts.
As the Wimo commercial version (79 euros) is well engineered and the cost of 2 of these is less than the price of just the rotator if I was using a rotatable beam, I may well buy the Wimo version.
A big wheel is also available for 70cms and 6m. The 6m version is a BIG wheel! The 70cm version is tiny.