If I had a Spekie and it was fitted out for LiPo - then I would use that. But I don't. I have radios .. JR and others that are all NiXX based ... they all work ... they all give me long use time .. they all stand on shelf and hold charge for good period ... and all charge as designed via the charge socket.
You know, I do find it odd that the Spektrum charging system is designed to automatically stop charging a lipo when it is fully charged yet can't do the same for the NiMH battery that comes installed. Once I found this out I made a charge lead and would only charge the original 2000mah Nimh with my smart charger which unfortunately didn't help the battery life. A flying buddy of mine just sold his DX6i and bought the DX7s and is already experiencing short battery life and excessive self discharge. There are several 4000mah lipos out there that drop right into the Spektrum Tx which is designed to use either and in this case are well worth it.
I work way too much so when I get the opportunity to fly I take full advantage of it. I can say that so far I'm really impressed with the lipo. Not because it's a lipo, just that it holds up forever. Had the stock battery held up half as good I would have gladly saved that $50 (well, I'm sure I would have spent it on something else RC).