The Hay King is specifically designed to not disturb the top soil. As stated, the coulter is designed to slice the top (however many inches you set the 3 pt depth) soil and plant shoots (for Bermuda especially since they have such and I have such). In clay soils, in arid times the shank disturbed soil opens up and makes a crack which fills with water and fertilizer when applied, getting such down in the root zone.
Anything that disturbs the soil to a depth will create a "pan" of some sort. So the question is, how much pan can you tolerate/need. I had a neighbor with a 3 shank "pan breaker" and the shanks were about 3' long and made of 1x4" solid steel (rembering best I can), tapered on the bottom with a replaceable foot. Had a 105 White with duals/weights and he said it ran in A1 (his lowest gear) and took all day to go nowhere. Since most tillage implements run a few inches or so, this implement surely broke up the existing pan.
I entertained the idea of the spike toothed drum and almost bought one till I realized that when my clay gets hard it probably wouldn't penetrate and wouldn't cut Bermuda shoots like I want. I wasn't looking at a 10k# unit, the small ones readily for sale on the www. I know they make some really complex units that cost a bunch of money. For a BTO it's no big deal. I'm not a BTO.
As with any implement, you need what YOU need, not what is good for others. Good luck.