On the knots versus shackles arguments, one must remember why
OH&S type publications mandate shackles.
Shackles can be tested and manufactured to set standards and thus such "rated" hardware
becomes a fixed known standard.
The tying of knots OTH is more subjective and cannot be controlled by the writers on the manuals
and therefore remain an unknown value.
However, a well tied knot
(and appropriately de-rated) would be IMO better than an unknown non-rated shackle.
If you can trust your own knots to secure your boat and take the enormous loads on running rigging
, you should be confident going aloft on a knot
, but if you are unsure of your ability with knots, go for "rated" hardware
Knots are cheaper but only if done properly