Does anyone have one of those hiking type baby carriers? The ones with the metal frame- is it worth buying or borrowing one for carrying a 15 month old?

Background: we are going to be visiting some national parks. Big kids are 4 and 6, so any hiking we do will not be too long or too strenuous, but DH and I are going to be carrying the baby plus water, and the usual "stuff". Would it be worth it to invest in one of these or will we be fine with an Ergo? Any opinions/advice welcome!