I'm based in the US now and the a/c I fly has all the goodies* for weather avoidance: Garmin 540, Avidyne MFD, XM weather, radar and stormscope. Weather downlink/uplink vs onboard radar provide different capabilities.
Satellite weather compilation is not 'real time'. The information is usually several minutes old. Sometimes as much as 20 mins or more. The composite data give a greater area of coverage than onboard radar. It's best used for more strategic decision making and not for penetrating an area of TS eg should I fly west or east to avoid that line of storms and how far?
In comparison, on-board radar has limited range and view but the information is immediate. It's much better for penetrating an area of weather ie go left or right around this cell then head over there around the next one.
To add to the mix, a lightning detector only detects lightning so no good for non-sparking weather. Beneficial when used with radar to discriminate between TS & 'just' heavy showers.
*It also has a fuel totaliser & JDM engine data monitor so even fuel monitoring & calculations for diversions and/or alternates is much, much easier. Jeez, to think I used to happily fly IFR with just an ADF for radio nav with a max. two hours between fixes and a watch + fuel gauges for endurance
. Who'd ever want to go back?
much later...
To round out the equipment description, it has a traffic information & alert uplink from participating ATC outlets, stereo inputs into the intercom from both cabin & cockpit, prop syncrophaser and a Panther modification that gives increase MTOW and more HP. It's only a Navajo but I used to fly a Kingair that was steam driven in comparison.
Something I failed to mention about the XM Wx: It includes METARs in the downloaded data so you can even check the weather at airstrips that are out of ATIS range. *Very* useful when the weather is filthy and you need to monitor where is still available.