I consider these compressors as disposable and have never purchased a warranty on one. Now, having said that, I do see where the warranty could be peace of mind, if getting it repaired or replaced was an easy process. Since I've never purchased a warranty, I have no experience on how well they work.
With relation to the YH vs. the GX, I have had 2 of each, both YH's failed after about a year of use, both GX compressors are still going strong! One (GX CS4) is about 6 months old, but the other (CS3) is still going strong with it's new owner and it's over 2 years old.
For you're use, the GX2 should fill your airguns with no issue, however, will fill them much slower that the YH. If speed is not an issue, I would recommend the GX over the YH just based on my experience.
The GX CS2 is on sale at GX Pumps for $298.00, with free shipping. There is also a 10% off code (GX10OFF) that will drop that to $268.20.
Only Available in USA and Europe GXPUMP CS2 Portable Airgun Compressor, 4500Psi/30Mpa,Oil-Free,Powered by Car 12V DC or Home 110V AC with Adapter (Included), Paintball/Scuba Tank Compressor Pump with Extra Moisture-Oil Separator. Oil-Free & Water-Free & Built-In Fan Cooling for Long Life ...
gxpumpofficial.com
If you do plan on filling your 100ci tank, I recommend investing in a one way valve, such as the one made by Best Fittings.
It will prevent the back pressure on the compressor as it fills the tank and helps when you have to take a break to allow the compressor to cool off during a fill session. I have a 90ci tank and have used the CS3 to fill it on a number of occassions using that oneway valve.
I found the valve at SUBMOA for less than it was purchasing direct from Best Fittings just because the shipping charged by Best Fittings seems quite unreasonable for such a small part!
Best Fittings One Way Valve for Compressor / BEST Fittings One Way / Non Return Valve Quick Coupler Compressor Connector Decanting / Compressor Connector with One-Way Valve
submoa.co.uk
Hope this helps...