This is a bit of a sensitive question. I believe there are some court cases (e.g. regarding maritime transportation) and sometimes divergent guidelines from national authorities but I am not familiar with all the details. The relevant EU regulations do not really define what “comparable conditions” are. Some of the disputes around this came from replacing a plane by a very long bus or train journey or asking people to use the landbridge over England instead of a direct France-Ireland ferry.
Importantly, on the face of it, the right to re-routing is not a right to make your own arrangements and demand that the operator pay for it. It’s an obligation for the operator to find a solution with a bit of leeway as to what that solution might be. That’s where the “comparable conditions“ kick in: the operator does not need to offer travel under the exact same conditions but merely “comparable” conditions. Yet, there is no fine and no clarity on what exactly you can do when an operator fails to respond in a timely manner or to provide a good solution.
I will note that all these regulations also make allowance for long-ish delays. There are nuances depending on the regulation and each of these rights is independent but for example the rights to assistance and compensation for air travel only kick in after a 2 to 4 hours delay. The bus passenger right web page you linked to even implies that having to wait up to two days is acceptable, as long as the operator pays for a cheap hotel and meals.
So the clause about “comparable conditions” is there to protect you against an operator trying to force you to accept a very inconvenient route or less comfortable means of transportation and not to define a list of solutions you could choose from. Getting to your destination in time by any means necessary is not really part of it and it’s hard to argue that the next plane or bus on the same route would not be “comparable conditions”, if the operator would offer it.
Some comments also rightly pointed out that the relevant EU regulation might not even apply to this route. While Flixbus is a long-distance bus operator (and doesn’t seem to have noticed they can get out of trouble in that way), Vienna-Bratislava is too short to qualify.
For all these reasons, I think an appeal based on the definition of “comparable conditions” is doomed. Your best bet is to focus on the lack of information and support on the ground (this may be actionable even in the absence of any passenger rights legislation) or perhaps turn to travel insurance, as suggested in a comment.
Credit:stackoverflow.com‘