I had terrible trouble with my Yeti 400 (Purchased in the EU) the inverter was faulty on delivery, apparently this was common with a certain batch. Either way i had to return it for a refund. But the product was fantastic.
The one issue i did notice is that the display didn't register any input until the input wattage reached around 50Watts, so if you trying to charge from a small panel then you may have issues, as there is no real way to determine if the power going into the unit is making its way to the battery, unless you place a meter inline.
IMHO i wouldn't use the goal zero solar panels i would go for folding solar panels with Bosch or equivalent cells in, as they are more accurate in there specified output. For the 400 i modified the goral zero 8mm input cable and added a anderson connector to it, and this can go straight into the solar panel output, you must keep in mind the rated input on the charger on the 400 as i think its low, so anyone expecting to add a 300W panel to it expecting it to charge quicker will be disappointed, the same applies to the Yeti 1250 which i am soon to purchase, i believe that is limited to 250W unless anyone knows any different?
Regards from the UK
Edit the Yeti 1250 has a maximum 240 Watts Solar input, anymore and the power is dumped and not sent to the battery.
Edit the Yeti 400 has a maximum 120W (combined) input, which i believe is the limit of the 8mm connector, and the same would apply to the Yeti 1250.