Unfortunately this is a completely useless method for keeping slabs or anything flat. Things like this were called Snake Oil at one time. The tensions in the wood will bend small steel profiles like this with ease. There are reasons age old methods like skirts are used and even then there is no guaranty against warpage. Properly dried and processed wood is the beginning especially for slabs.
Edward, Thank you for sharing another great project! The whole project is well thought out and executed, but IMHO, the sanding and finishing is especially superb!
Please keep posting these. I know I learn a great deal from your pursuits and I'm sure there are others who share this sentiment.