focal length – APS-C + speedbooster vs full frame

I own a Nikon in DX-format (Nikon name for APS-C sensor, crop factor ~1.5) and I’m considering buying a 50mm prime lens soon for it.

Of course, because of the crop factor, such a 50mm lens would give me a 75mm effective focal length (by which I mean when compared to a full frame body). I have two choices, as I see it:

  • go for a 35mm lens instead to end up with a ~50mm effective focal length in the end,
  • go for the 50mm together with a 0.6 or 0.7 speedbooster.

The second option has the advantage that I’ll still have a 50mm lens if I decide to go for a FF body in the future. What are the drawbacks of a speedbooster really? From what I gather online, the only thing that could be bothering is that it shifts your aperture range towards low values (f4 becomes roughly f1.2 in my imaginary setup). And I would actually consider that a plus considering what I usually shoot.

What are your thoughts on the subject?