When we had pigs up to last year, we used Laverstoke all the time, just with slapmarks. If you are going to keep pigs for several seasons or more, I definitely think it is worth investing in a slap marker as it is so easy to do and you can just do it the day before they go. I reckon with metal tags Laverstoke require the two as they routinely slice the pig down the middle, so each half is then separately identifiable. On one awful occasion I got a couple of pigs up there, and realised when I arrived that I had completely forgotten to slap them at all so they had no form of ID whatsoever, but the lovely Polish blokes up there made an exception for that one occasion, rather than making me go all the way home, an hour's drive each way, to get them slapped.
Your piggies look fantastic and very happy - we used to keep Saddlebacks too, and like Kelly I am missing them like mad, a huge void in my life. But it had to be, so instead I follow what all of you are doing on TAS instead, and just love seeing such gorgeous pics.