My older (18
A lot of it is really personal preference and how your ds responds. I personally wouldn't have more than one potty chair per floor.
For when you're out and about, the portable inserts were bulkier than what I wanted to tote, BUT they are probably a lot easier to use when taking a child to the potty in public. My kids didn't like their potty seats, so they trained on the regular toilet (we used a toilet insert with one child). I just had my kids sit backwards on the toilet, to make it easier for them to get on/off without falling in. The downside is that when you try that on the big toilets in public, you have to totally strip your child of clothing which is a huge hassle. A toilet insert would allow them to just pull down their pants without having to strip completely.
The free-standing/disposable liner potty chairs are good in theory but they take up a lot of space in the car and would be difficult to use IMO. Unless you spend a lot of time on the road without a bathroom near, or at parks without public restrooms, or something like that, I don't know that it would be worth the hassle and expense for me. I don't think a free-standing toilet would be very convenient if you were in the middle of a store when your child needed to go potty. There have been a very few occasions where one of my children has suddenly needed a toilet RIGHT NOW while we were driving, but I just keep a few diapers in the car to be used as an emergency toilet in those types of instances (pull over to the side of the road and stick the diaper into their underpants).
I know some people would disagree, but I put my kids in pull-ups when we went out of the house while potty training (cloth underpants at home), so I didn't have to worry about accidents or running to the toilet every ten minutes. Once my kids were pretty well trained, then I let them use underpants when we were out of the house.
Good luck in the training process!
A, Hi and welcome to the Toilet Teaching board.
The previous poster had some great information for you. I also agree that it is a personal choice. The potty chairs can be moved from room to room, and the potty seat inserts. My preference was one potty chair to be moved around with us, and a potty seat insert in each bathroom. It will be the same thing for the travel potty if one is needed, there are some really nice ones out there. We had a seat cover one, and it was used once, it became more of a pain then anything else. Taking it out, and in the beginning stages when they say they need to go they need to go right away. That is my opinion of them. Please keep us updated on your DS progress.