I would say a free pen, cup or something when you sign up or hit say £100 would be a really good promo for customer and subliminal messaging. 
So many people now work on zoom/Teams type systems or would use at work and would be a longer lasting advert than a free share.
You could actually give to every verified forum member as they are obviously pro-FT and more likely to talk about the product if they received something from FT to potential new customers.
Talking of verified accounts, there was an idea about that 
[Feature Request 
] Verified User tag - Ideas 
- Freetrade Community
A store is a simple thing to do and just get another company to run the admin side, for a %, and free publicity. Really good open goal there for FT to shoot at.