I assume it is the high sugar content off brand cola they use. I like Rum and Coke, but can't imagine how bad it would taste with a cheap, off brand cola.
Theres 2 ways it can go... Nasty or "Wow, that aint bad." Wow that aint bad, can actually be a bad experience, and I know that from experience, lol.
Years back, when I first set out on my own, my fridge was pretty empty. I had a pizza, a Fifth of Jack, a 6 pack and some leftovers a family member dropped off, in the fridge. I grabbed the bottle of jack, and realized I had no cola to mix it with. I thought about drinking it straight, and was immediately hit with horrible flashbacks. So I pushed some stuff out of the way in the fridge and I found a couple cans of Minute Maid Lemonade Soda hiding in the back...
That stuff is SWEET (as in sugary), I mixed a drink in a water glass (like I said, I had just set out on my own in life, I didn't even have a shot glass or mugs) and sat down to watch some TV. Felt nothing after the first glass, so I mixed another (1/2 Jack, 1/2 Lemonade)...Nothing. Mixed another (3/4 Jack, 1/4 Lemonade). Still felt nothing.
At this point I stare at the glass and rant. "That lemonade soda is killing the alcohol!" So I mixed another potent batch of 3/4-1/4 and I make it about a quarter of the way into the glass when it all hit me like a freight train! Normally I would have felt something long before that 4th glass, and I have a suspicion that something about the lemonade soda turned the drink into a real creeper.