I've not yet started a game with the 5th Ed rules, but I already had the discussion with my players on why they should take a Burden - if they have the choice of getting the same +2 without a negative impact.
Having a Burden is a great RP opportunity, but it should feel, that it is a balanced option.
So bundling a Burden with the benefit of a Boon could be an idea.
So the choices would be like:
- get +1 to 2 attributes, or +2 to one
- get +1 and a Boon
- get +2 and a Burden and a Boon (without the additional +1 to an attribute)
That would feel more like a hard choice...
My players have a lot of RPG experience but little to none with D&D, and in the original Symbaroum it was easier to be very competent in you specific field very early.