I like the Soledi thread - it's not a very high quality thread, but as long as you aren't pushing 200 stitches in a row, it holds up nicely and is cost effective. I use the beige and the brown regularly. It freys very easily (it's braided, not a tri-cord) so make sure you melt your ends.
I was using Maine polycord for years but I found that the excess wax caused horrible discoloring on anything bigger than a card wallets when using natural colour thread. The wax on the thread picks up pigment. 30-40 stitches was a maximum in terms of a good hand stitch with Maine. For the a while now I've been running my Maine polycord through the feed on my 29K Singer with a bit of heat to clean up the excess wax for hand stitching.
This method helped A LOT with the colour but seriously, not even close to worth the effort. (I wanted to use up the thread I had left) I still use Maine's colored threads, but never the natural or white threads.
Soledi will still give you cheap looking stitching (not that the customer cares) - if you want to make your handstitching look the best it can, you'll want waxed linen - Somac 18/5 or 18/6, or try Barbour 18/5 18/6.