Sharing my experience on a recent BLR-AMS-SEA route where BLR-AMS was DL ticketed (M fare both legs) but operated by 9W. In a nutshell, I would not fly 9W on codeshare again unless there was absolute no other reasonable option. Reasonable includes 50% longer route and >6hr layovers in SIN or KUL. Will fly 9W on 9W stock if it was paid C.
First, no advanced seat selection. Ok, 9W policy, I get it and am ok with it (every carrier can set their own policy). However, not being able to check on my itinerary on jetairways.com after the tickets were issued was a warning I should have paid more attention to. Reject message was that 9W does not allow itinerary management on their site for a PNR ticketed by another carrier. This means, DL status wouldn't have mattered. At the check-in threshold, same rejection message so no online check-in hence no seat selection. Top that off, BLR airport needs proof of travel for that time window to get into the airport. Showing your itinerary may or may not get you in depending on the person at the entrance. Can't use the self check-in booths outside the airport either, again because it was DL ticketed.
Found my way inside with help from external 9W booth but agent would not check me in until 3hrs from departure time citing security check requirements and nobody could do the security check now. I was there about 6 hours early due to meetings completing sooner than expected and figured I could grab a drink and dinner at the airport, no luck unless you want to head back out or hit the coffee place (some starbucks equivalent). Eventually, at check-in time, the exact same crew that told me nobody was available for the check security were manning the passport/visa check lines and put a sticker on my (US) passport indicating my travel docs were in order.
Checked in, aisle seat (thankfully), 6 rows from the tail (A333). Asked about bulkhead, wing or anything closer to the front (bumpy tail rides make me nauseous), told there was nothing and basically waved me away. Boarded, took a walk just before door closed and found lots of open seats (aisle, window, middle) in the mid section with at least 2 rows in the middle column that were completely empty. Guess the agent just didn't want to deal with a seat change.
Plane and service were generally ok, about the same as other carriers, though IFE touchscreen wasn't very responsive (no big deal for me). Only vegetarian options left both times by the time they got to me so not so great for food experience. The airport and online experience makes 9W on DL codeshare really undesirable . Also, it's been just over a week and flight still not posted to my DL account.