It's totally up to you which tokens you choose, you can choose either D-tokens, which distribute dividends or you can choose U-tokens, which give a trader more favourable features, when trading on the platform. Or you can choose both - say 60/40 - as you wish.
Remember - it is a trading platform, and you use ETH when trading the instruments. You do not use U- or D-tokens for trading. You can trade on the platform even if you do not have tokens of Spectre at all. It's a free trading platform to anybody.