The advantage of this arrangement is no crossover, which is a big plus, no loss of power, no phase shifts, sound is coherent coming from one voice coil.
The disadvantages are limited frequency response on both or one end of frequency range, limited power handling, may require complicated and large enclosures to extend lower end.
Full-range speakers were historicaly first used on open baffle. Later in closed enclosures. Many variants of enclosures exist, their goal is to extend low frequencies. Some are more effective than others.
more backoaded horns
Another approach to one way speaker is the use of multiple fullrange drivers, like in line array or omni-directional speaker on next two pictures. There are some advantages, like increased power handling, pinpoint imaging for line array, spacious sound with large sweet spot for omni-directional speaker, but there are disadvantages too, like the comb effect in line array or too much early room reflections in omni-directional speaker. It all comes to personal preference.