The equipment is fantastic. It is so dead reliable, and so much like having utility power, that we don't even think about it anymore. No flickering in the lights when the A/C compressor kicks in (yes, we even run a 1.5 ton central A/C unit with it), it will handle significant overload for quite awhile, has no de-rating based on temp, and the entire system (solar controllers, inverter, AGS, ComBox, SCP) integrates better than anything else I've ever seen or worked with.
The 24V unit is only available as 4.0 kVA. The comparable 48V unit (XW4548) has a few more watts capacity and is the same price as the 4024. I suspect they don't offer a 4.0 kVA 48V unit because of the 4548.
You can set the allowable voltage and frequency limits for your genset, and get the XW to sync up with it. BUT that "dirty" power is passed on to your loads too. So it pays to buy a decent generator. If the genset is operating and it falls outside the allowable voltage and freq that you have set, the XW will disqualify and take over. Then it will analyze whether or not the generator is stable enough to re-sync with it. If the genset is operating in allowable limits, no load, the XW will re-sync with it and load it according to what you have the Gen Support level set to. But if there's a rat's nest plugging the air filter, within milliseconds it will "spit" the genset off and take over again. It will continue to try this several times (I think six) and if the genset don't straighten out and play decent the XW will shut it down (assuming it is controlled by the AGS) and flash a warning (red light) with a message on the SCP telling you that the genset is no good and you need to fix it. If you have a ComBox it also sends an email to your cell phone telling you that the genset is fricked up and it disabled further auto-starting of it until you get around to fixing it.
The XW is a big transformer-based inverter. Just the transformer in it weighs about 65 lbs - more than a whole Outback FX-series, or Magnum PAE, inverter. Big transformers like that eat up quite a bit of power when idle because there's a lot of copper in it. But that copper mass is also why it can handle significant overloads for a long time, and why it has such rock stable power output. Ideal loading is 20% rated continuous capacity or better. So if you buy one and your normal loads are only 500-600 watts don't buy a 6048. Buy the smaller one. The smaller one will still handle your biggest loads using gen support, and be more efficient for the >90% of the time that your loads are at baseline.
The thing I like about it is that my wife can be doing laundry with the washer and electric clothes dryer going, decide to make a pizza in the oven (electric range) and turn that on, the well pump can kick in, and the inverter still handles all this, along with all the other stuff going, even though it is grossly overloaded. It waits for one minute and if something don't get turned off it fires up the gen, warms it up and syncs with it, and transfers 4.0 kVA of the load the genset to reduce the load on the inverter back below rated continous. It is so seamless that we do not even think twice about it anymore.
So overall I consider the big XW to be pretty much the "Cadillac" of off-grid power. It is a proven design that has been around for many years, they rarely break, Schneider Electric now has a tech support dept that far outshines anything Xantrex ever had, and the integration of the system components has not been matched by anybody else. I am extremely pleased with it and not a single complaint because the XW has basically given us utility-scale (and quality) power in an off-grid situation. And it does it without having to stack inverters, and buy a lot of extra batteries to power stacked inverters.
I put the pencil to it long ago and genset fuel for when you need overload capacity is less than 30% of the cost, long term, that JUST the extra batteries would cost to power stacked inverters at the same capacity as the XW+Genset during gen support operation. The longest I have ever seen the genset run (logged by our ComBox) is 3 hours 53 minutes one time on gen support. And that was for Christmas when my wife had EVERYTHING in the house fired up to cook Christmas dinner for the whole family that was there and using a totally electric kitchen to do it. So the genset burns about .65 gal/hr at that load and we used 2.6 gallons of gas that cost like $10 bucks. Big whoop, ya' know? If you look at it realistically, you could spend $4 Grand on more batteries, and $3,600 on another inverter to power all that. But what is the chances that you can recharge those batteries on RE power later? Nil to none. We used something like 32 kWh in that four hours, and even with all the expense in extra batteries and another inverter, there is a greater than 95% chance the genset would still still start to charge batteries.
And in a nutshell, that is why I designed our system to use gen support as an integral part of it.