My attempt to pull information together on these two TDSZ2 subjects
Q factor is the outside measurement of the crank arms where the pedals screw in. Road bikes measure around 150mm, mountain bikes around 175mm, the TDSZ2 with stock arms measures 210mm.

Q factor is controversial, some says it is much ado about nothing, others say less is better. For sure wider Q means you scrape your pedals earlier when cornering.
For those you feel the TDSZ2 Q factor is excessive there is an easy way to reduce it to 182mm, use Bafang BBS cranks arms. I bought a pair for $27 from thinkpan on ebay, they are sold a lot of places. They fit perfectly on the TDSZ2.
Chainline is the distance of the center of the chainwheel to the center of the frame. Chains work best if they pull straight. Derailleurs move the chain side to side, so the chain can only pull straight on one cog, any other cog and the chain is not pulling straight. Opinions differ, but my experience is that things get scrapey (noise, chain wear, bad shifting) at 18mm offset. As bike manufacturers add cogs the dimensions change. They make the chains narrower, tighten cog spacing, etc. http://www.sheldonbrown.com/cribsheet-spacing.html. By the time you are trying to make 10 speeds (4mm cog spacing and 37mm cluster width) work on a single chainring you need your chainring to be centered really well on your cluster. I would really want to be within 2mm of centered, more than that and it is better to stop using the worst rear cog. Fewer speeds don't necessarily help, they have more cog spacing and the chains are less flexible, but 7 speed spacing (5mm cog to cog and 32mm overall cluster width) is more tolerant, 5mm off is pretty OK with 7 speed spacing. And keep in mind that the TDSZ2 is stronger than you are, the engineers weren't designing for motors, at most they were designing to a tandem with two strong riders.
Tongsheng specifies 50.2mm chainline http://www.tsbicycle.net/products_detail/productId=136.html
View attachment 3
I don't trust the cross-section drawing because it shows 50.2mm with a flat chainring but... I measured 50.7mm on my unit so 50.2mm is close, 50mm is standard on mountain bikes, 145mm is standard on road bikes.

The stock chainring is dished 5mm. Using a flat chainring (the spider is 110mm BCD (bolt circle diameter) so they are common) increases chainline 5mm, so really the stock 42T chainring is the way to go for most cases. 50.7mm is really not bad, so the talk of an inherently terrible chainline is not true when the TDSZ2 fits the bike well. But the TDSZ2 doesn't fit all bikes well (and good guidance about what you need in a frame is not easy to find before you buy, I'm trying to give some of that here). So:
50.7mm applies to a 68mm BB. 73mm BB bumps it up 2.5mm
The gear reduction housing almost touches my chainstays, and I have steel road chainstays which are the most compact.
View attachment 1
You really need the TDSZ2 main casting to seat against the bottom bracket tube. If it can't because the gear reduction is touching the chain stay you will stress the casting in a really bad way when you tighten the M33.5 lock nut. Don't do that. Use shim washers until the casting seats (increases chainline), grind the casting locally (do at our own risk) or dent the chainstay (only on a steel frame and also at your own risk).
So it is really nice if it fits your 68mm bottom bracket frame. OK, so what can be done about chainline if it too large? (too small is easy, use a non-dished chainring).
1. (easy and cheap, 1mm). Use 10mm inside diameter 1mm thick shim washers McMaster Carr 98089A385 gives dimensions to look for.

2. (harder, not expensive, 3mm) I haven't done this because my chainline is OK, but I am confident it would work. The 42T dished chainring is steel so it has decent thread strength if tapped. The chainring nut is on the inside, If the nut is removed thicker spacers can be used. Tap the existing 10mm holes 7/16-20 UNF. Drill out the spider to 7/16 inch (11.1mm) taking care to keep centered. Use 10mm inside diameter spacers (it looks to me like up to 3mm would work) and assemble directly into the chainring. Grind or shim the bolts to exact length so they don't protrude. If you go metric I think you really want to go fine thread (M12x1.25), even though it is less common. It should be OK but the chainring holes will need to be drilled to 10.9mm before tapping. 7/16-20 is easier if you can get the tap and bolts.
3. (easy, $100, 5mm). Buy the custom 10mm offset 42T chainring made for the TDSZ2. http://www.electrifybike.com/store/p65/42_Tooth_Narrow%2FWide_CNC_7075_T6_Chainring_%2810mm_offset%29_for_TSDZ2.html
4. (variable difficulty and results) Fuss with your cluster. Freehub cassettes can be manipulated, check the web. You can put nine 10 speed cogs on a 7 speed freehub body. You can stop using the worst cog. You can reduce the clearance from the smallest cog to the dropout by moving spacers from the cluster side to the other end of the axle (no bad effects so long as the chain doesn't rub, but you have to re-dish the wheel). Bafang BBS people have a thread that covers a lot of this. https://endless-sphere.com/forums/viewtopic.php?f=28&t=84097
My take overall is that Q factor is easy to make way better, and the chainline is not bad if you have a good frame fit. But if you don't have a good fit it can be a real problem. If I was thinking whether to buy I would be pretty confident if my frame was steel, my bottom bracket was 68mm wide, and my chainstays did not look wide compared to the picture above. If the frame fit looked iffy I would ask questions on this forum before buying.