Flixbus?
 

I don't see much about it on this board. Is there no point in using it? We will be in Brussels and Amsterdam (middle spot tbd) from Nov. 30-Dec. 13 and plan to take a lot of day trips. Was just wondering what people's experiences were with this service.

Flixbus is cheap, and that is about all you can say about it really. You are sat on a bus, with a lot of other people for a long period of time.
Trains are not that expensive between Brussels and Amsterdam and that is what I would personally choose unless your budget is very tight.
For days out just use normal public transport.

A fairly established bus company. It does the job of bringing you to a destination.

Flixbus buses are pretty typical European long-distance buses. They're operated by local companies, after all. You get a nice website and app for booking trips all over Europe on a moment's notice, but the actual travel experience is the same as it has been on buses for decades.

It's actually not dirt cheap, but it's often cheaper than long-distance trains, especially if booked last minute. It can also be convenient for some trips, particularly travelling to/from airports that are not on the mainline railway network (or on any railway), like Cologne, and for cities that have indirect rail connections only (like Rome and Siena, for instance). The overnight services between cities that don't have direct sleeper trains are often the most time- and cost-effective way of travel, if not particularly comfortable. For instance you could technically do a day-trip (2 overnight journeys, 1 day in between, no need for accommodation) from Amsterdam to Copenhagen and back, if you can endure it.

In the Netherlands and Belgium, it probably won't make sense to take a Flixbus over regular the extensive regular public transport network of trains and buses.

Unless there is significant savings, I'd opt for train over bus.

Not having train options in Slovenia, Croatia, Montenegro, and Bosnia I had to rely on their local bus system. Often was being operated by Flixbus. It was fine. In my experience, the drivers were usually on time (but border crossings complicated that - not their fault) and buses were normally fairly clean.

The nice thing about Flixbus, is that they let you book your seat far in advance, and if you are travelling solo, you can reserve an empty seat next to it for a pittance (the same with Flixtrain that runs limited schedules on some popular routes). You can book the front row seat, and then pay a couple Euro to block the seat next to it, and have it feel like a private taxi with a giant window. Some busses have table seating, with frontward and backward seats facing the table, so you can play poker together.

The limitation is, of course, that it is a frickin' bus, and it gets stuck in traffic if that is its (your) fate, and you can't get up and go to the dining car for a fresh tapped beer, you have to bring your own bottle of beer with you.

I've used them twice (Zagreb to Maribor / Linz to Cesky Krumlov) and they were fine, comfortable enough, departed and arrived pretty much on time. We booked online in advance. I always prefer train to bus, all things being equal, but sometimes buses make more sense for particular routes. Site getbybus is good in some countries, offering multiple bus providers.

I've used Flixbus from Basel to Frankfurt airport. Never again (there was major work going on with the train route; it would have entailed multiple train changes and significant delays). The bus trip took over 7 hours; the normal train trip takes less than half that. The seat was not comfortable and when we went through rain showers (there were a few) water dripped onto my seat. The storage space in the passenger part of the bus is minimal, so even a carryon bag has to go in the cargo hold (just an fyi, that wasn't a problem for me but might be for someone else). I should have simply purchased a last-minute flight from Basel to FRA.

Check out rome2rio.com for comparisons. i never plan a trip without rome2rio.

Flixbus
 

September took flixbus from Ljubljana bus station to Budapest bus station for $18.00. Six-half hour bus ride but no issues. Checked flight but too much of a hassle with layovers.

We used the bus to go Chamonix - Geneva - Annecy - Lyon,(stopping in each place).. We used the bus because the trains were 3 or 4 times the cost and took longer (changes, scheduling). I think two of the routes were FlixBus and two were Blablacar buses.
I recall that one of the Flixbuses had a broken seat and we had to move. Other than that the seats were comfortable, the buses were clean and the rides were punctual. I didn't have the ticket purchasing app for Flixbus and had to get help to buy tickets, which seemed weird.
None of the buses had a toilet on board.