I need to know if Kryolan Eyebrow Plastic works better than Spirt Gum Adhesive?

depends on what? a lot of the models I know use "bikini bite" as a swimwear bottom adhesive.

Kryolan eyebrow plastic (alone) was created to cover one's brows.

Spirt gum adhesive (alone)- was made to "adhere." 

Technically, they are two different products with two different uses which equals a comparison of apples to oranges.

Is the intent to cover brows?  If so, to use spirit gum, one also needs wax and sealer (there are more steps to cover the brows...)

Time is a factor as well, one may look better than the other, but the other may last longer.

Personally, I find that wax, sealer and sprit gum look nice - but it is a medium I am used to using - someone that uses Kryolan probably favors that instead. I have seen one artist actually use all of the above items at one time.

The cheaper route would be to go with Kryolan (about $6 or $7 dollars a stick).  When it comes to using spirit gum, it's about $5, plus the wax plus the sealer...prices vary on quantity / brand for all items). One will also need a remover.

When one says "better," the question is "better how?"
What exactly do you wish to use either product for?  What is the duration of wear? Is the question about the ease of use?

Vague inquiries on opinion are difficult to answer.

If one is looking to adhere some little rhinestones or something very small, use some cheapie lash glue - the cost is about $2.00 plus tax where applicable.