The main difference lies in how cashback limits are applied to your transactions. Shops with limits have a maximum cashback limit of €0,50 per 30 days.
The total cashback you can earn from them is limited and calculated on a 30-day rolling basis. The total limit is €5 (for example when you earn 10x €0,50 per merchant) in the first 3 months and €2,50 after that.
Shops without limits (no "coin" icon) do not have these limits, allowing you to earn cashback without restrictions.