Or sometimes TGVs in TGV clothing. And IIRC SNCF and DB charge differently at times
Normally, Duplex TGVs operate on the Paris-Stuttgart route and ICE on the Paris-Frankfurt route. This allows our German friends to enjoy the Neubaustrecke landscape from the upper deck of a Duplex!
It is true that all Alleo (the SNCF/DB cooperations) trains operate on a compulsory reservation basis. However, unless I am mistaken, Frankfurt-Paris ICEs have the typical Bordbistro for travelers who fancy sausages and beers. (1)
The Velaro (ICE3) is a good, solid piece of rolling stock, but I do agree that Eurostar have given it an utterly horrid interior.
At the risk of sounding
chauvin, even though the Velaro/ICE3 is a good train overall, it is
not on par with trains based on the TGV design when it comes to dynamic stability and comfort at high speed. The TGV bogie & suspension design, which was improved in the mid-1980s after the first few years of operational service, provides an extremely smooth ride. This is particularly impressive on Duplex TGVs, considering the height of trailers.
In addition, in their early years, the operational record of ICE 3 train sets on French-style 25 kV LGVs with ballast-laid track was abysmal. Simply abysmal. Remember that Eurostar suffered a 2-year delay before they could enter service.
(1) I know that the on-board food selection on TGVs is terrible... but I cannot say I am impressed by the stuff available in DB trains.