Yes, adhesive-lined 3:1 ratio is my preference too, e.g.
RS adhesive lined heat shrink
When properly fitted, products like this will provide insulation that is equivalent in durability and dielectric strength to the original cable insulation. Many basic heatshrink products have a thin wall and are much less durable.
With 3:1, choose a size about twice the diameter of the joint; this allows the tubing to shrink by 50% (which doubles the wall thickness) but leaves a margin of shrinkiness so that it grips firmly. On large joints especially, preheat the joint so that the adhesive doesn't cool and solidify too quickly when it makes contact. Once cooled and set, it should be difficult to peel off the joint even with a knife or cutters; like normal insulation you can hack into it but it stays stuck firmly in place.
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Re the tool, I suspect a mismatch between dies and splices. Are they SWA branded|? A properly crimped splice should be completely impossible to remove in any way at all. Under tension the cable should stretch and snap, leaving the joint intact.