Good to hear you experiences on the Go-find 40, you are correct in it not feeling like the most sturdy detector out there, bit of a trade off for the compactness of the detector I guess, though in the long term it will be interesting to see if they stand up to some abuse.
You really have to drop the sensitivity back a fair bit to get near any play equipment, though lose a fair bit of depth in doing so unfortunately - not really a fan of the square concentric coil. It certainly isn't the deepest detector around, and will often just sound off once rather than repeatable signals on deeper coins, probably better off as a detector for cherry picking shallow modern coins more than anything. In fact I'd go as far as to say my Ace 250 hits on deeper targets more positively, and offers a more expanded discrimination range vs the 4/5 segments on the go-find.
As I have mentioned previously, it is what it is, and that is a cheaper simplified detector for the kids, or for those just starting out to have a bit of fun with or to get acquainted with the hobby. If you want something to grow into as you become more experienced, there are other detectors on the market in a similar price range that offer more flexibility, accuracy and performance.
My Go-find 60 was mainly bought for the car for odd opportunity, though it needs a bit more of a run before I decide whether to place it in the keep/sell basket.