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 €2.5 (for example when you earn 10x €0,50 per merchant).
Shops without limits (no "coin" icon) do not have these limits, allowing you to earn cashback without restrictions.
Reward rates vary by merchant, you can find a full list in the Auto Reward section of the app. You are eligible to receive up to €2.5 per 30 days from when you first connect your bank account. You're eligible to receive up to €0.50 per merchant, per 30 days.
After enabling Auto Rewards for the first time, a special one-time reward will be given for your past purchases. Based on all of your eligible Auto Reward transactions over the past 90 days, a maximum of €2.5 can be redeemed in your Cashback Sock. (This option is only available in NL app version)