I tried using the free version of WPC Shared Stock plugin with variations of two different products and it didn't work. Has anyone been able to use the plugin successfully? 

Same here. Just tried it.
Added 3 variants to a group (initial stock 500), multipliers are 10,12 and 14.
Put one ore more of these variants in my cart, finish the order, complete the order in Woocommerce - group stock is still 500.

That's basically what happened to me. I had stock in both variants. Put several of one in my cart and completed the purchase. The one that was purchased debited, but the other one did not. Overall stock did not change either. I needed it to work right away so I purchased a different plugin.

@Deb French: May i ask what you purchased instead?

Group Stock Manager by WooExtend

Hi :-)

Thanks for the effort!

I updated the plugin, deleted my testgroup, added a new one with 3 items in it (3 variants of a single prodcut) and made a testbuy. Still no change in the overall stock. And i do not see the "managed vom shared stock" message in the details of the variable product... 

The stock history log of the group shows nothing but "group created".

EDIT: It seems to be a problem with variable products. If i add a single product to the group everything works as intended. If i add variants of a variable product (not the variable product itself), they do nothing.

EDIT2: I could narrow it further down:
- I have a variable product (Trouser) with three variants: Trouser S, M and L.

- I add these three variants to my group (garment roll with 500 units) and multipliers of S=10, M=12 and L=14. Expected: i sell a Trouser M = group is reduced by 12 units. -> Nothing happens.

- I additionally add the variable product (Trouser) itself (multiplier of 1, because it is never sold - only the variants) = it almost works: The group stock is reduced by 1 (but should be reduced by 12, if i sell a Trouser M).

Hope that helps?

WP 6.94, WooCommerce 10.7.0, Plugin 1.1.2

Some screenshots attached ...

THAT was quick! :-)

It now works as expected.
One more happy customer. One more PlugIn sold. :-)

Thank you again.

@Deb French: Thank you. Will have a look, but so far i am happy right here. :-)

Unfortunately, I already paid for the other plugin. Good to know for future.