Not too many people think very highly of Castrol Syntec (except for the 0W-30 grade imported from Germany), so they would be even less likely to recommend Castrol Syntec synthetic blend (at least in terms of price/performance).
You would do much better with Walmart SuperTech full synthetic, or make your own synthetic blend with 1-2 quarts of a high quality synthetic and the rest conventional oil. It will probably be at least as cheap as using all synthetic blend, and a much higher percentage of synthetic.
I'm one who does think highly of Syntec and SB. They both run very quietly. I've never done a UOA on either, but if the old GTX drive hard did well in my trail Jeep, I imagine that the SB 10W40 was stellar.
In my experience Syntec runs quieter than Mobil 1. Then again, so does Q-TP, Q-HP, PP, etc... Does that mean more wear? I doubt it. It does add piece of mind though.
I liked it. The UOA came back excellent and when it was $10 a 5 qt jug, excellent oil.
At whatever it is now (last time I looked closer to $20) not worth the $$.
Same with GTX. When Pennzoil is $12 and Havoline DS is $11 GTX @ $14.50 is way too much.
GTX is excellent oil but so are the others. There is not a bad SM oil out there IMO.
what is the reason they don't think highly? is it the PRICE? or is it the performance of the oil?
The price is definitely a factor. But Syntec is the original Group III synthetic, the first company to claim that hydro cracked mineral oil can be called full synthetic. Castrol advertising has always been a bit controversial, even today. Edge appears to be a very good, although very expensive, oil.
Bottom line is that it always cheaper to make your own synthetic blend. Just use 1 or 2 quarts of a full synthetic and you will be way ahead of the synthetic blend oils that have very little synthetic oil (Group III or IV) in them.
And like I said, if cost is a factor (it usually is) then the cheapest full synthetic is still way better than a synthetic blend. Walmart SuperTech is a very good synthetic to use for your entire fill, or to make your own synthetic blend.