Interior foam guns worth it?

I have 3 or 4 cars coming up that have been transporting 2-4 children for years and have never been cleaned.

My main concern is the upholstery. All of the vehicles are fabric with most of the car seat area being one solid sheet of spilled juice/milk/vomit/ and food.

I've already talked to the owners who are ok with some possible discoloration and damage that these levels of dirt and cleaning may come with.

My plain of attack is to vac/tornador as much as I can. Then use a degreaser with an extractor for the main load. Before I bring a drill brush into play.

I've learned the wonders of the tornador and wondering if anyone has any experience with foam guns for upholstery. Because I have these cars lined up, if the foam guns for upholstery are worth it, I feel now would be the time to invest before I have to go do them.

Any feedback either way is greatly appreciated!