I realize Ikea is not exactly known for their high quality, but thought I'd ask b/c these are "similar" to the flex slats at Sovn, etc. but at a fraction of the cost- $200 for a king. An interesting option to potentially pair with either the Sovn Willow or some other bed option. I didn't love the solid wood (non-flexible) slats, but do seem to like the flexible slats in general.
As an example- the Sovn Willow King mattress only is $2,600. That plus this $200 base is $2800. More manageable.
Of course, if this foundation is total garbage, than discussion over.
I think that the Ikea slatted bases are one of their better values. While I haven't used them personally, and I don't think they are the same quality as the slatted foundation that BE outlets sell, they do seem to be made of good materials and there is no doubt that the prices are great.
A few things that I would be aware of (although you probably already are) ...
They need to go on a bed frame of course and they are very thin and closer to a bunkie board in height so your mattress will be lower.
I would also make sure that you measure your bed accurately because they are a little bit of an odd size.
They can be difficult and time consuming to put together according to some reports I've read (the slats aren't easy to get into the cups)
They may not flex in the same way as the foundation under the Sovn so the mattress may feel or perform differently with a different foundation.
All in all though ... I wouldn't hesitate to buy one if I was in the market for a lower budget tension adjustable base.