Ok, lets first start on the cateory of lubrication. Lubrication is a method to reduce friction. There are two types of friction relating to the cube. These types are static and dynamic. Static friction relates to the amount of energy required to
start moving the object. Dynamic friction relates to the amount of energy needed to keep it going. But, a successful lubricant needs to increase the smoothness while reducing the static friction.
After we have that cleared, i will answer the questions to the best of my ability.
What is the difference between 30K and 50K oil?
The 50K is more popular and thicker, this means it will last longer. If you are looking for price, the 50K will last you longer, therefore reducing the (Price=AmountSpent)*UsesBeforeRunOut ratio. In my opinion, the 30K Oil seems to make it run faster, too fast. I literaly lost control every 4 turns, having to re-adjust.
Will it melt my cube?
No, most Silicone oils will
not melt your cube, but beware with Jig A Loo as it can melt your cube if you don't fully disassemble it.
Is it a better alternative lube for my cubes?
Yes, it is really an amazing lubricant, and it is more cost efficient than lubix.
Is there a difference between Lubix and Traxxas?
Yes, there is a tiny difference, but it is usually not noticable. Most professional cuber use Lubix for the very small edge over traxxas. Lubix also comes with a cool syringe.
For the last question, I personally just thing it is something that does not matter that much.
I hope you have read this post because it took a lot of my energy. As a conclusion, the 50K wt oil is better.