I have had my Siboasi S4015 for two or three weeks now and like it a lot. Duration of use on one charge of the 30-Amp lithium-ion battery is amazing. On one charge I used the machine for six hitting sessions that lasted about two hours each, though the throw wheels were not spinning for the entire two hours. And, yes, the S4015 is one of only two or three machines that has internal oscillation. I ordered my machine with only an external battery, as I wanted two batteries. Since the charge time for one battery is 10 to 12 hours, I wanted easily to be able to use the machine while the other battery is charging. I do not think it is possible to have the machine with an internal battery and use an external battery when the internal battery has been depleted, something about how the internal electronics are wired. Without an internal battery, the S4015 weighs 26kg.
Tell Siboasi that your two choices are the SP and the S4015 and that you need a competitive price. The price from Siboasi used to be about USD1550 exclusive of shipping. Then prices went up in
July to around USD2100-USD2200. I think at that raised price there might be periodic sales that get the price back down to around USD1550. For the sake of comparison, the S4015 is in class with the SP Smart, which is about USD2100 to USD2200 shipped. This is a price that Siboasi should be able to meet or beat inclusive of shipping.
I do think the S4015 is more compact and runs more quietly than the SP. It stores easily underneath a table in my living room.
The S4015 is dual-powered AC/DC. The S4015 I received has an internal 120v/220v switch.