Pro-ject speedbox: Is improvement worth the $ ?

The Speed Box only provides the user to change speeds at the push of a
button. It does not have the ability to fine tune the speed to compensate for
deviations in pulley, platter, and belt tolerance.

Since your motor is an AC synchronous motor, it is not dependent on stable
ac voltage like a dc motor but relies on the grid's 60 hz frequency.
Fortunately in the US, the 60hz frequency is highly regulated and controlled
and does not deviate like line voltage. A true motor controller will have the
ability to change the frequency thus allowing a fine tune of the motor's
speed.

I wouldn't purchase a Speed Box unless I frequently changed between 33
and 45 records. Spend your money on a real motor controller, not a switch
box.

I used a Speedbox 2 on my Debutt III and 2 Xperience and in both cases sound stage became more 3d, bass articulation was tight and it yielded blacker backgrounds. I use Proac and B&W speakers which are both fairly revealing so the differences were clearly audible.

That said Pro-Ject has excellent speed and pitch stability in stock form unlike certain older Regas and a few other brands. I used Linn tables for 2 decades (Lp12 and Axis) and those were always spot on for speed and pitch so I wanted the Pro-Ject to be comparable. Of course the difference you get from something like a Lingo on a Linn is far more dramatic, as it should be for that kind of money. But I think the effect of the Speedbox is easier to hear than say the TT PSU that I use for my Rega P5.

I have not tried the better Speedbox SE but the base model is definitely worthwhile and very reasonable price wise.

I had an MM7 for a few years, and when I added the Speedbox I noticed immediately the improvment in image stability and pace. Do yourself a favor and add this essential piece of gear to your MM table.

I saw a difference with my Project Xpression, more bass

Not really, Brf said it best. You will be better off putting the money on a better cart.