I am a long time MC and auto/kart racer. Tried the traditional my first few games, and I felt uncovered. For me, the only concern is protection. It comes down to the padding, not the shell. Other than TW, there is nothing adequate for me. Since I am used to full coverage, and there is the added benefit of side, top, and rear coverage, my selection is HSM.
Using TW Zap pads in an AS 2500. While the stock padding was certainly comfy and no doubt meeting NOCSAE, I could too easily (IMO) push, with a finger, to the limit of the padding. IMO, our "normal" hits are at or beyond the NOCSAE test level, and we , if done properly, have no chance to move to deflect, so we need padding to better slow the energy transfer than NOCSAE padding.
The TW pads are the first time I have felt like I had adequate padding for umpiring, when compared to the products available in a MC/auto helmet. Have had several concussions (not from umpiring), and as I think someone already stated, if I get another, it will be my last game for at least a year.