I really like TRL and used it with my daughter when she was learning to read. We both appreciated the ease of use and the large, kid-friendly font.
I have another child that is in the learning to read stage and I went ahead and purchased a new TRL book for her to use. I had thought about using our current copy with my younger daughter, but I did let my older daughter write in her book when she was using it originally. She had also placed a sticker on each page after it was completed, so it is now a precious keepsake of her learning to read journey. I'll have my younger daughter use her book the same way so that when she is older she can look back and see her reading progress.
I would imagine however, that most people who use TRL for more than one child probably preserve the pages so that the book can be used more than once.