My wife and I took 3 different day tour out of Edinburgh. Great thing to do, I recommend them! Our tours were on the small buses that hold 16 people. This is the way to go. No toilet onboard. But they stop often for potty breaks. I did note that all 3 times the bus was full. And this was mid September.
So, I recommend you get booked 3 or 4 weeks ahead of time. Just print out the confirmation and show to the driver/guide. They will have a list of names of those that are going as well. I also recommend you make a dry run a day or so ahead of time so you are sure where you need to go for the pickup. Rabbie and Heart of Scotland are located near each other.
Which Rabbie tour did you take. I will be in Edinburgh next September and am thinking of doing a couple.
Can you give more details about which tours you took?
We took the Hairy Coos tour and highly recommend it. It's free - no hidden charges. You pay what you feel the tour was worth at the end of it. The tour was extremely informative as well as catching many of the highlights heading to the Highlands. https://www.thehairycoo.com/tour/1-day-free-scottish-highlands-tour-from-edinburgh/
If we get back to Edinburgh on our trip coming up next year, we'd do it again - it was THAT good!!!