There may be some nay-sayers against the switch that my want the option under 120M, and also there is some extreme optimists that are saying it may reach 165M - 170M that's why I decide to put option for those extremists for 170M+. And yes, I also think that 150+ is also very optimistic, however there are more than a few people here that think switch can pass 150M lifetime (as you can see, we already have 2 people voted for it). This option is for them. 5M increments at this point in switch sales doesn't make sence. We are still too far from 130 or 140 or 150 to make exact prediction within 5M to be accurate (whereas with 15/20M it's more easier). Also 5 options for this question is small number. On some old threads people put 10 options or close to 10 options on polls like these.
I guess 5m increments might be a little too granular yes, certainly for the higher end of the scale. And yes some people vote with their hearts so having the 150m-170m option is fine (it would just take a concerted effort by Nintendo to push unit sales, something which they have never been that bothered with at this level)
And yes that's what I meant for the poll, I haven't made any threads so I dont know the system but if the site lets you put more than 5 why not use them when you are encompassing a sales range from 120m to 170m.