Note: All of this is for pre-8.2. The changes in the Type's damage per round have changed the possible earnings ceiling, presuming Wargaming did not change the credit multiplier. I don't have any reason to expect it has, but I also have no evidence it hasn't.
Yes, the premium everyone loves or loves to hate. I daresay one of the most polarizing vehicles in the game, one that has made me bundles of money. But that statement bothers me. Not because it is flippant, I quite enjoy flippant, but because it is vague. "How many bundles?" I ask. So I set out to find just that. But before we get to the numbers, the tank itself. You may skip to the section labeled "Real Numbers" if you're already familiar with the vehicle or just don't care what I have to say. Either is fine.
In the real world the Type 59 is a Chinese carbon copy (licensed, not stolen, this is when China and the CCCP still liked each other) of the Soviet T-54A, an improved version of the T-54. In its basest form the Type 59 differs from the T-54A only in that it lacks an infrared searchlight. In the game, however, the two vehicles are quite different. Their hull and turret shaping is virtually identical, true, but things such as armor thickness, horsepower, cannon performance, view range, and various other factors, both visible and hidden, differ greatly.
For these reasons it is more meaningful to compare the Type to its direct ancestor, the T-44. They are both in the same tier, they have the same number of hit points, and have roughly similar matchmaking brackets (Type 59 gets 8-9, T-44 gets 8-10 out of a max of 12). The vehicles themselves share virtually identical hulls, although the glacis armor of the T-44 is 10mm thinner, and the side armor 5mm thinner. These are not particularly notable differences, though.
There is a common misconception that the Type 59 has a more aggressive slope to the glacis plate, this is not true. My personal theory is that this is a belief left over from when the Type had very low matchmaking and frequently encountered vehicles that would not otherwise see a Cold War-era WarPac MBT. Their first experience with the style of vehicle was with weapons that had little hope of penetrating, but when they encountered the T-44 it was only after they had graduated to more powerful tanks with superior weapons. The 60° slope means the difference in thickness of the plates is only 20mm for a round coming in perfectly horizontally. Given the low profile of both vehicles it is unlikely for such a path to be taken, so the effective difference in plates is likely <20mm. This is in stark contrast to the T-54, which can have up to a 40mm advantage over the Type 59 and 60mm over the T-44. This is all without mentioning the normalization of AP and APCR rounds.
The Type 59 does have three notable advantages over the T-44.
Barring those, the Type 59 is essentially inferior to the T-44. The T-44 has a significant horsepower/ton advantage over the Type, allowing it to maintain greater mobility. One of the chief frustrations I feel when driving the Type is how anemic it can feel at times. You just don't get anywhere as fast as you would like to in a medium. The T-44's gun is also superior. The rate of fire advantage is quite small, but the LB-1 has significantly improved accuracy and aim time. This makes sense, as the Type's gun is essentially an improved copy of the venerable 100mm D-10T cannon that serves as the first 100mm cannon the T-44 can mount. Also, the Type carries only 34 rounds of ammunition to the T-44's 56. It is not uncommon for me to find myself critically low on ammunition, as the Type 59's full load of ammunition averages only 7,820 damage. In comparison, a tier 8 heavy can have up to 1,650 hit points, requiring fully 23.5% of your ammunition to dispatch without assistance.
Now, don't get me wrong, in no way do I think the Type 59 is a bad vehicle. I've driven it more than any other tank in my inventory (got a lot of stuff to buy, after all), and it is a solid tank that is capable of contributing to the team, just a little less so than the other tier 8 mediums. If for whatever reason you feel the need to dispute this with me, I'll save you some time in looking up my stats, since people seem in love with doing that. The credit multiplier is the entire reason for the existence of the tank, so enough pontification from me, on to the numbers.