Just as with radios, there are several different types that run different software so best do some research before rushing off to buy one.
They are useful for connectivity to DMR as well as D-Star and Fusion. You can use them to access Brandmeister and many Phoenix talk groups using the DMR Plus network (connect to IPSC2 Phoenix F server) – more on this via the “DMR Plus” menu – https://dmrguideuk.wordpress.com/dmr-networks/phoenix/dmr-plus/.
They are handy to access a network where there are no repeaters nearby or if your local repeaters are connected to only one of the two major DMR networks. Also for those that can’t access a repeater either due to location or being unable to put up antenna. Also some are well suited for mobile use so you can stay connected no matter where you are. If you are away on holiday or business, you could use one in a hotel, connected to the hotel wi-fi or using mobile data. Powering these devices can be done via a phone charger, usb or a power bank so you can basically take them anywhere.
They are personal low power simplex devices which do not require a NoV. The output is in mW and one only need use a radio (preferably a handheld) on low power since they need to be located within a short range of the user however they are best located away from items such as computers and not too close to where you are transmitting.