We use Archer for our brand kit. It would really help to use letter box but it isn't efficient for me to have to edit all the letters in Adobe or Word

Agreed. We are not permitted to use fonts outside of our brand kit, and this results in having to edit letters after they're generated. We use calibri, which is a very standard font, as well.

I also have this issue. While our style guide prefers the use of Agenda, we are able to substitute with Open Sans.

Would also love to have this feature added as the font I need to use as per my company's style guide is not available. I am able to copy and paste it in with the font I want but it doesn't always work and involves a lot of fiddling around with the template to get it right.