A bit of a strange choice as they are quite different but ignoring cost (UK based so Atom pricing is better) which would be your choice?
I have had a Cycleops Hammer and H2, both of which I have enjoyed in the past few years.
I would happily go for an H3, but curious whether going for the Atom would be a worthwhile step.
Easier adjustability - both myself and my wife can get comfortable on it, without having to change bikes.
Increased stability - High power out the saddle type intervals with less fear of breaking.
I did an out of saddle sprint on my S Works Venge last year and I bent the skewer, frame jumped out and crunched back down. Fortunately just superficial damage.
170mm cranks - I usually run 165mm cranks
Bike Fit - Not sure I can get the Atom to exactly match my road bike position. The fit calculator says that the max range is 75mm for forward adjustment, and they calculate that I will need 101.
Also not sure it will go low enough at the front for me, as the minimum is a range of 571mm.
Space - I have plenty of spare bikes, so having the Atom won’t save me 1 bike worth of garage space.
Any thoughts or opinions on the two?