I took a quick look at Sunstar, Ian, and I hope you don't mind me saying I paid less than half of what you will for one simple reason: you're being ripped. Royally. In my opinion, of course. All of what follows is only my opinion; your parameters may be different.
Some of those Sunstar bits look like they're straight out of the Bafang factory; this is a not uncommon experience in pedelec conversions; the QSWXK motor fancied by many here comes in a wide range of kits packaged by various suppliers, under a variety of names, at a range of prices, some of them amazing; the one I recommended and many bought was the cheapest competent package deal with a fixed price from a reputable, reliable dealer.
Some of the Sunstar engineering won't cut it in kindie mechanic school, for instance an anti-rotation tab you have to bend -- how many times can you bend it before it breaks off and makes the whole unit unserviceable? -- this is a joke!
If there is a torque sensor, you want to ask to see the patent. Bafang also claims a virtual torque sensor, and if Sunstar's bare motor supplier is indeed Bafang, this may be what they're talking about. The reason the Chinese don't have a proper torque sensor yet is because Bosch and Panasonic have the patent sewn up and aren't licensing it to every Tom, Dick and Harry. Where did Sunstar get the technology? I wouldn't pay extra for this socalled torque sensor without checking further into it.
Even if the Sunstar torque sensor is real, I don't know that I would pay more than the price of a whole Bafang BBS kit for it again, because that's what the pricing comes down to. I have a more powerful motor than you're contemplating, and there is definitely more torque, but I haven't been thrown over on my head yet, though before I got the hang of it I lifted the front wheel a couple of times on the throttle. But you're an experienced cyclist. Maybe if you were some nervous nellie with zero experience I'd say, sure, the torque sensor is worth doubling the price of the installation, but even so I'd probably say, ride the various models first, compare for yourself.
The controls and facilities of the Sunstar model I looked at are pathetic, and that's being polite. My previous motor was conservatively chosen because it was well established, which also meant that it was a couple of generations old. It had several useful facilities more than the Sunstar, which makes the Sunstar really outmoded. The Bafang BBS packages available in England have controls facilities that leave the Sunstar for dead.
Of course, it might be worth it to you to have something different (I drove Citroen SM for several years despite the nuisance of constant repairs -- but nothing short of a Bentley Turbo could match the crosscountry times of those Citroen, and the Citroen was more comfortable), and on the forum you'll be appreciated and celebrated as a pioneer taking one for the team... And I might just be an old fogie who is outmoded enought to expect serious value for serious money.
Some of the Sunstar accessory bits may be of better quality than supplied with the Bafang, for instance with the Sunstar, according to the video, you get branded cranks (presumably because at the elevated Sunstar price, the "free" Bafang cranks look a bit cheap). But for the difference in price you can buy many sets of cranks...
Sunstar pricing is a wonder to behold. The Sunstar SO3 kit is priced at The Electric Transport Shop at £800 without a battery. Eeowwwww!
The comparable 250W Bafang BBS-01 kit is priced at Eclips Ebikes at £320 without a battery, with what appears to be better operating peripherals (throttle, control facilities, modes and tools). That's 40% of the Sunstar price... Eclips Ebikes, from whom I bought, and a few other people on other fora too on my recommendation, is at
http://eclipsebikes.com/bafang-8fun-bbs01-drive-250w-motor-p-1102.html. You can import the same kit for less from China if you want to take your chances with swingeing customs duties and import taxes and perhaps even a special "anti-bicycle dumping tax(1)" and fees added willynilly by the couriers; I decided the risk wasn't worth the small saving.
(1) According to literature on the Irish Customs netsite, this could be 48% of the value of goods, transport, brokerage fees, import duties and VAT on all of that, and then the 48% on top of everything (taxes on taxes? -- shiver my bones!), by which time you'd be better off buying a Range Rover and adding to pollution.
Sorry about this, Ian. If you're in love with the appearance (bright ali bits) of the Sunstar and the money isn't important, go for it. But if like me you insist on value for money, I really do think a close comparison is in order, and some hard questions about what you're actually getting.
