First time using this today after struggling with a 30mm AF nut on my campervan suspension , both undoing it and then tightening it back up to lock the two fittings together.
On a large (30mm) spanner it certainly adds a substantial amount of leverage and saved my shoulder . It grips the spanner well and did not slip off. The gaps of the hooks where the spanner fits are large enough for a big spanner.
For an occasional use tool it was worth the £15ish from Amazon .
No negatives from me and I’m sure it will get used again.