After having converted several music notation fonts to SMuFL I do know that it is a lot of quite complicated work!
And I am not talking about creating new glyphs but only about the conversion to SMuFL.
For example it is not always straight forward to find out which from the huge amount of available glyphs in Bravura are actually used by Dorico.
A lot of Bravura glyphs (there are so much glyphs in Bravura because it is a model for SMuFL) are simply not used by Dorico and this is nowhere documented.
To create the necessary metadata is also not an easy task.
And here again it is also not always clear which metadata are used by Dorico.
Abraham Lee from Music Type Foundry did a great and huge work to port some of his wonderfull fonts to SMuFL.
Of course it is unfortunate to find out that a specific glyph is missing for a specific situation but at some point Abraham will surely add the important missing glyphs.
The personal use license for a MTF font is $0.99
I would say it is a very moderate amount and the best way to try the fonts and to see exactly which glyphs are available.
I also would like to add that Abraham Lee did years of non-profit work for the LilyPond community!
All his fonts are also freely available for LilyPond.
Though this has nothing to do with Dorico I think it is important to know where MTF comes from.