The Sig Sauer MPX was to be an updated version of the MP5. Side by side you can see how similar they really are. They even kept the name similar to the MP5 but simply nixed the 5 for an X. Both chambered in 9mm. The MPX is a pistol with an adjustable Sig Brace to mimic the collapsing stock of the MP5. The Sig MPX differs though in its piston driven action vs the roller delayed block back operation of the MP5. Sig went with an AR-15 style configuration so it has an AR15 style charging handle. That is one of the weak point of the MPX and where the MP5 shines even though it is decades older. Forward charging handles are easier and faster to manipulate than the AR style charging handle. Recoil on the MPX is astoundingly minimal and both suppress very well.
With the recent explosion in popularity of pistol caliber carbines, something Nathan F. has expressed dislike over, there are many options of MP5 clones if that is what you desire. The MPX can be purchased for just a little less especially if you shop around you can occasionally find them for a great deal.