The SD-9 and the SD9VE are very similar. The internals are the same. Here are some of the stock numbers of the various models (including .40 S&W models):
11587 - S&W SD9™ HI-VIZ® Sights Academy Exclusive
11907 - S&W SD9 VE™ HI VIZ®
11908 - S&W SD40 VE™ HI VIZ®
11993 - S&W SD9 VE™ HI VIZ® Gray Frame Finish
11994 - S&W SD40 VE™ HI VIZ® Gray Frame Finish
11995 - S&W SD9™ Gray Frame Finish
11996 - S&W SD40™ Gray Frame Finish
11998 - Model SD9™ Flat Dark Earth Frame Finish
11999 - Model SD40™ Flat Dark Earth Frame Finish
120400/120900/220400/220900 - Model SD9 & SD40 (with metal sights)
123902/123402 - Model SD9/40 VE - MA Compliant
(I'm open to corrections if any of this data is wrong or incomplete)
The SD's are great value for the money but they do have a long, heavy trigger. Therefore, all SDs and SD9VE/40VEs benefit from the Apex spring kit and the Apex "Action Enhancement Trigger," sold separately or together by Apex Tactical.
It is a debating point whether you need to improve their triggers, considering they are self-defense guns. It also can be debated whether it is worth buying them at their low price and adding the springs and trigger modifications at extra cost, or if it would just be better to start out by buying the M&P for about $100 more.
The original SD-9 came with a black slide and metal front and rear sites. The current SD-9 still has the black slide, but comes with the HiViz fiber optic sights. There are versions of the SD with black, FDE, and gray frames.
SD9VEs come with a choice of two sight systems, "plain" plastic or HiViz fiber optic, and have a plain (silver colored) stainless steel slide and either black or gray frames.
The nice thing about SD's and their sights is that they are interchangeable with M&P sights, so that you can upgrade to metal sights if you don't like the plastic ones; plus lots of companies make after-market sights for the M&P - Trijicon, Ameriglo, Warren, etc.