Yes, the main advantage of both is lower commissions if you compare them to Wealthsimple/Wealthify/Nutmeg or any roboadvisor.
The following is not financial advice but just some publicly available information.
They offer a range of funds you can invest in. Their account fees are 0.15% of the invested capital, capped at £375 per year. On top you need to add the fees for the fund you choose. Their very popular LifeStrategy funds charge a 0.22% fee. Thus, in total, you are paying around 0.37% if you are below the cap. The choice of funds and investments is limited to few Vanguard-branded options.
They are one of the cheapest stockbrokers on the market I could find. Their fees are very low and they also have a list of ETFs for which you pay no commission (subject to few terms and conditions). DeGiro trades everything you can think of.