As far as I know, there is no difference other than magnification. With the 2x you have 140-400 mm, with the small 98 - 280 mm. The speed also decreases with the factor. The converter turns 2.8 into 5.6. Since your lens already covers the range 98-200 without the converter, I would recommend the 2x. Note: the thing also works with the 105 mm macro. With a 210 mm macro you can turn a mosquito into a sperm whale. However, the handling is extremely demanding. Have fun with it!

Thank you very much for the answers. I should perhaps have specified my question a little more precisely. I was only concerned with the technical differences between the products on offer. I was confused by the different presentation of the images, but the same price! Since I need the converter exclusively for documenting a swallow colony (occupation of the nests, frequency of approaches, etc.) and the equipment is fixed on a tripod, the autofocus is not relevant. I should also be able to cope with an open aperture of 5.6. And I hope the loss of sharpness is kept within limits. An alternative would be a 400 or 600 tele with f 2.8....But if I were to order such a lens here, I would have to add the cost of a divorce...and then it would get really expensive! I have therefore decided to go for the 2x converter. Thanks again!

I can only concur. The 2x probably makes more sense. I have to say, however, that I only use the converters on fixed focal lengths, as the loss of quality on zoom lenses was too great for me, even on the 70-200/2.8.