I've been using this for a while now and really like how its expanded my FSX "feel". Here is the promo text:

This utility includes numerous features to expand your take-off and landing experience in FSX with enhanced sounds, visual effects and more.
External conditions and those of your aircraft will affect factors such as aircraft icing, runway performance and braking, and further features include additional head movements, enhanced sounds, charts and information screens all controlled with an easy-to-use configuration tool. Sim Physics X is a multi-function application which includes numerous unique features in one product to expand your take-off and landing experience by bringing you enhanced sound and visual effects.
Features include realistic ice accumulation on your aircraft, improved braking behaviour that varies depending on runway conditions, numerous enhanced sounds and a new head movement system.
A beautifully designed user interface allows you to customise your experience and also provides information on airports, aircraft and weather.

Its $19.99 at Just Flight right now. I haven't done any "shopping" around to see if there are any better deals. I had a conversation by PM here earlier this week regarding my 15th AF Italian adventure in another post about the 461st BG and Torretta AAF in Italy. The B24s had a problem with mud on their airfields in Foggia so with that not being mentioned as an enhancement of Sim Physics X I wrote to them and received a reply today. If simconnect recognizes those conditions on grass, clay or dirt and transmits this information to Sim Physics X (which is how that works) it will simulate mud making it more difficult to taxi, takeoff and land just like it does ice and snow. I am anxious to try this out later and see if FSX simconnect will do this. BTW I don't get any perks or commission from FSPS LOL! With this and REX Ultimate I feel I get a pretty good environment simulation.