Start with the best tool on the market
Best tool currently on the market. While I'm climbing in Switzerland now, I've spent most of my time climbing mixed and water ice in the northeast US. These tools are absolutely amazing for leading. The swing is fluid and confident. They stick on a single swing even in cold conditions. At first I was worried I would drop the damn things, but I've had cold days where I couldn't feel my fingers and bad falls where my junk got re-adjusted... I never dropped a tool. Once you switch to leashless you will wonder why you didn't make the transition earlier- switching tools and placing screws suddenly got a lot easier.
I've also climbed with BD Vipers, BD Cobras, Ergos, Ta-ka-toons, tech wings, etc... they've all got there strengths. If you want an alpine or "do everything tool" get the Vipers... if you want mixed and water ice, bite the bullet and buy the Nomics- they last forever and you won't be drooling over them after you bought some cheaper tool.