I think they are robo-landline dominant. That means they’re ok, but I’d add a few points to whatever they say their MOE is.
How many people do you know who don’t even have a landline anymore?
I imagine folks without landline phones are in the older category, so the polling skews toward Trump. And the unpolled, cell-phoned younger set, it is claimed, gravitate to Sanders. So it’s not such an important number for the primaries, but for the general election, where the voter turnout skews toward the older generation and the young ‘uns don’t bother to vote.
Rasmussen has a pretty decent track record. Within the past year or so, cell numbers have been made available to mass marketers/pollsters. I think these pollsters now manage to capture quite a few who have only cells.