IMO, the audio Technica new IM series build is abit bulky. For example, the IM50 to me, is pretty hard to achieve both a good fit and a good seal. Takes some effort to do a tip mod so that the IEM can sit nicely. But the body of the IEM will still be bulging out unless you have got a large ear canal.
The SE535Ltd is pretty good in terms of their build quality and as well as fitting and isolation. However, IMO, MMCX connections can result in occasional sound cut off when you're using them for jogging as the connectors can swivel.
I do not have any opinion or views on W40 as I have not tried them yet. But the W4R is sturdy build and provides a good seal and isolation as well. To me, i prefer the old Westone pins to the new MMCX connectors.
Sonically wise, I can only comment on W4R and SE535Ltd only.
W4R houses a more balanced sound signature with very smooth treble extension, lush and sweet vocals but with a mid bass bump. It is more of a laid back presentation which may get boring over time. Separation on W4R is very good and soundstage is above average as well.
On the other hand, SE535Ltd houses a mid centric sound signature focusing on vocals. Both male and female vocals are portrayed upfront which sounds very lush and intimate. Puts you like 2nd row of the hall. W4R is more laid back probably around 4th row of the hall. However, treble extension on SE535Ltd is not as extended as the W4R and I find them slightly metallic occasionally on certain tracks as opposed to W4R. Bass on SE535Ltd hits slightly deeper without the mid bass bump. But I find the quantity of bass is more on the W4R. If you're planning to EQ SE535Ltd, the bass can be made better. Separation and detailing wise loses out to W4R. Soundstage is pretty much the same as W4R if not slightly wider. SE535Ltd is more fun sounding due to it's more engaging vocals.
From reviews and impressions on the W40, it can be seen that it is slightly ahead of W4R. Probably W40 maybe a better option than W4R.
Hope this helps! 😊