The Wiki article for tremolo claims it's the most popular style, especially in Europe and Asia. Yet when I was researching harmonicas last year, most of the discussion I saw was for 10 hole diatonics, with chromatics a distant second.
On https://www.harptabs.com/ there are many more contributions for the diatonic than the tremolo. Most of the tremolo tabs are from one poster.
The tremolo harmonica is different. No bending is required. In fact, bending is difficult with the double reeds, and rarely done.
The tremolo is therefore easier for tunes than the 10 hole, because note bending is not needed. All the notes are there. The tremolo is not so good for blues, as note bending is a big part of the blues harmonica sound.
Bending, if I recall correctly, was developed by blues players to produce notes that aren't normally played on the 20 reeds.
The first challenge for a beginning player is to blow or draw one note at a time. With a wider separation, that is probably easier on the tremolo. Bending is a more advanced skill, but essential to a blues sound.