I see pluses and minuses here.
Plus: Speed, no stops at edgy banlieue stations, far less chance of problem fellow passengers.
Minuses: Cost, getting to Gare de l'Est, (I assume) Not having the convenience of catching the RER B south of Gare du Nord for a no connection trip to CDG.
Saving 20 minutes on a trip to the airport will matter little to many passengers, and I expect the popularity of the new train will hinge on other factors.