This was my experiences with both mascaras:
The Maybelline Colossal claims to volumnize your lashes. It carries large bristles and semi runny formula. I gotta say, I was not fond of the scent. I was bothersome by it. The mascara did add volume, but weighed down my lashes when I curled them prior to application. I don't have a good opinion on this one.
The Cover Girl Lash Blast claims to volumnize also. I has a wide wand with short rubber bristles. It doesn't look appealing at first, but after application, it does MAGIC. LOL. It doesn't smell, it volumnize and seperates the lashes. The formula is thick, but it does not make your lashes look like spider legs. And it does not weigh down my lashes. I am very pleased with this product and it is my current favorite mascara.
Maybelleine Colossal: 2.5 out of 5
Cover Girl Lash Blast: 4.5 out of 5
These are my personal experience and opinion with each mascaras and they were purchased with my own money.