Tubes or bellows increase the minimum focus distance, so you can get closer to your subject than you could with the lens alone. But the angle of view of your 50mm on extensions remains the same, AFAIK.
The difference between the two, in the range of situation where they can give you the same magnification, is thus one of perspective. So yes, the results are "similar" in terms of magnification, but no, they are "different" in terms of perspective (cf. a portrait shot with a 24mm v. one shot with an 85mm).
With the teleconverter, you could fill up the picture frame with the flower, from a distance of, say, 2m. With the tubes, you could fill up the picture frame with the flower, from a distance of, say, 0,5m.
I suppose that the people those who use both TC and extensions together do so because their subject require to keep a certain working distance, and they do not have the money to buy the more expensive, longer-focal macro lenses (Nikon, for e.g., has a 50mm, a 105mm, and a 200mm).
At least that's how I understand it.