I bought a TK35, primarily to use for travel, in particular for spotlighting wildlife. Firstly it's a great light and, as described in detail elsewhere, a great mix of flood and throw. Thing is though, for my purposes the throw wasn't perhaps quite as good as I was hoping for (for instance I was using it to scan hillsides in Scotland for wildcats - something that was going to be a futile task at the best of times!).
For walking in woods etc though, the beam is great.
However, when the TK41 came out soon after I decided that I'd have to give it a go - based on the extended throw and runtimes, and, primarily for me, the fact that it runs on AAs (I was using CR123s in the 35, don't have 18650s).
The TK41 certainly does have a longer throw and slightly narrower beam profile. This throw I think suits wildlife watching. Runtimes-wise it's definitely a step up from the TK35, though the trade-off is the size difference. To be honest though, this doesn't bother me though as actually I find the TK41 easier to use due to the UI and switch position. It's also now easy for me to hold the TK41 under my binoculars to do long range spotlighting, which due to the shape of the 35 wasn't possible. The TK41 doesn't seem particularly heavy - it just won't go in a pocket unlike the TK35. The 41 also doesn't get as hot as the 35 in my opinion.
Anyway, both great lights, but for me the combination of factors detailed above meant that I've recently sold the TK35, as I couldn't see the need for it alongside the 41 (I'd probably rather have a good 2AA light to accompany the TK41 for backup). If you've got 18650s however, I think the 35 becomes a much more attractive option as a great compact multi-purpose light for travelling. I like the fact though that I can guilt-free use the 41 when I like knowing I can just charge the Eneloops again - rather than thinking that's another few quid needed for CR123s...