It's a bundle of a Universal ticket plus a voucher for the Mears shuttle, which is worth $20/person. So if they really have a 1-day ticket plus shuttle for that amount, it's a great deal. But when I visit DU's Universal ticket page, they are charging $147 plus tax and handling for a ticket with no shuttle, or $165.78 plus tax and handling with the shuttle voucher. Are you sure you're not confusing the ticket with no shuttle for the one with a shuttle? If not, and they really are giving you the shuttle for free, then it's (mostly) a no-brainer. The shuttle isn't super convenient, so some people would take a cab over a free shuttle. Not many, but they are out there. It's a time/money tradeoff.
If the bundle is actually more expensive than just the ticket, then the question of whether to buy the bundle is really just a question of whether the shuttle is the best option for you. If you have 3 or more people, a taxi is typically a better choice for WDW to Universal. With 3 it's a tossup which will be cheaper, depending on traffic and where you're coming from in WDW, but the taxi is MUCH more convenient and quicker. With 4+, the taxi is almost always cheaper AND more convenient. With 2, the shuttle is cheaper, but I personally would still choose the taxi because the total difference is going to be like $20-$30 overall, and I would gladly pay that for the extra convenience. Your time/money tradeoff may be different.
And the absolute cheapest bottom-line cost is sometimes a single-day rental car, even after you factor in parking charges and a gallon or two of fuel, but only if you can get a great deal on the rental.
There are a lot of sources for tickets, but it's rare to find any kind of great deal on a 1-day, so get it from wherever makes sense to you.
