That radio shack clamp meter certainly gets horrible reviews, and one glowing review by someone who might be into bestiality.
I understand wanting to find the cheapest product available, but So often this tactic winds up costing so much more. It seems some many got online forums with the cheapest possible product, then want to find somebody who says it works 'just fine' and wants another person to justify their purchase.
The Drok ammeter/voltmeter combo requires one to join 4 wires to the Shunt, two big, two small. With regards to wiring up the whole electrical system in a Van, wiring this device up is cakework. If One's prospects of wiring up the Drok successfully are too Dire, then perhaps one should not be rigging up their own electrical system.
Clamp on Ammeters are great, I use mine daily, but a permanent Ammeter that displays charging current into the battery at the flip of a switch is so enlightening as to battery state of charge.