No matter what your router or mesh kit is capable of, you'll still be limited by your ISP's max speeds. If a gigabit connection isn't available from your provider or current plan, a mesh kit won't be able to help.
However, if you're using an older router that isn't capable of handling higher speeds, then upgrading will boost your speeds. Plus, it'll likely help you support more devices with more reliable connections. Before you upgrade, learn why your Wi-Fi is currently slow.