Advertised speeds are plan descriptions, not a personal guarantee at every hour in every home. Fibre offers often state both download and upload speed, such as 250/250 Mbit/s. Mobile broadband offers may show a maximum download speed, such as 150 down or 1000 down, but real performance depends heavily on reception and the device you use.
Data allowances matter most on mobile broadband. Capped plans can be enough for email, light browsing or a backup connection, but video streaming, gaming downloads and frequent video calls can use a lot of data. Unlimited mobile broadband removes the monthly allowance issue, but you should still check any fair-use wording with the provider.
Router details are easy to miss. The published plan details used for the examples above do not consistently state router rental, router purchase, delivery charges or return rules. Before you order, ask whether the router is included, optional, financed, rented, or required for the advertised speed.