We have a few Firesticks, which can do streaming via the channel's normal app like iPlayer, ITV Hub, My5 etc. Not all the Freeview channels seem to have apps, and not all apps seem to have the option of streaming live broadcasts. In addition, I think iPlayer might be geo-locked by IP.
Particularly on the lower end and older Firesticks, some apps are a bit sluggish - even powering on the Firestick at the wall can take several minutes before it becomes usable.
Much like a Smart TV, you install a (usually free) app from the Amazon Fire store, and once installed, you select this app from the Firestick's home page, so iPlayer for BBC, ITV Hub for ITV etc. I've not had it yet on Firesticks, but imagine like Smart TVs, there comes a time when the apps become incompatible with older devices and stop working.
In my recent experiences, Roku is every bit as sluggish as the original Firesticks, although that was a NowTV one, so might be that Uncle Rupert sends out the oldest, cheapest shite he can

I have issues with Wifi where I live (long story), so I find with the Firesticks that I have to buy an HDMI extension cable to lift the Firestick above the TV in some rooms, in order to get a solid Wifi connection, else the TV shields the signal a bit.