i have found it to be an excellent experience very easy. i have done it twice in the past couple of years and took advantage of a very early crossing around 5am so you can get to disney nice and early on your first day.
your first day and last day of tickets is calculated into your stay cost assuming your on site and booked rooms and tickets with disney, we arrived around 11am french time so got nearly a full day on day 1 and stayed to around 4-5pm on the last day before heading home. this wasnt driving at any major speeds crusiing around 65 70 most of the way and stopping for at least half hour for toilet breaks and a coffee at a services.
even if you book the save tickets it says they are only valid for ur allocated travel slot however if i have arrived early enough i have been able to check in to earlier trains at both folkestone and calais free of charge sometimes by several hours earlier. this is not advertised so is not an official benefit but pretty sure they like to fill up trains if there space to reduce queues and stop trains getting delayed at peak times
its also great for taking as much or as little luggage as you want or may need as ive never done a summer trip but can hear the weather can still be as bad as mid winter so having space for coats and things may not be a bad thing plus doesnt matter what you buy big or small gifts or delicate things your worried of breaking on a checked bag on a flight.
i would only consider getting the eurostar as another alternative to driving these days as my current car is not as comfortable for long journeys as the last time i did it
