couple of questions

[scorehouse]

when you get a unit that has (20), (10), how do you keep track of how the number is depleting? also, if a parenthesis unit is available but you delay using it for the following battle/scenario, does it remain a parenthesis unit or become a regular part of your available equipment without the parenthesis. thanks

[dalfrede]

If you go to your purchase screen you will see the number of strength point remaining(10)(3).

It becomes a part of your regular units immediately. But 'infinite' replace arrives only when the unit becomes generally available.
Some units such as 'Dicker Max' are only prototypes and are never generally available

[scorehouse]

do you think these units r worth using since their strength is easily depleted unless u r being really cautious?

[Kerensky]

do you think these units r worth using since their strength is easily depleted unless u r being really cautious?

This is extremely situational. Some units are fantastic to capture and deploy, because they are plentiful enough to acquire, and stay relevant long enough to be useful.
Getting your hands on a bunch of high armor Matilda IIs early in the African campaign helps a lot because of their extremely thick hides. A good T34 tank is as better than any German armor of the time, especially with that 6 movement, and later T34 models are just as good as any long barrel Panzer IV, but again have that extra speed which is very important.

But it all depends on your gameplay style. There's a big difference in playstyle from direct combat players who take commander traits like Panzer General and Killer team and someone taking more utility traits like Deadly Grasp and Trophies of War.