For what it's worth...
I like the sunuke bokken - a bit pricy but very durable, especially the early batches. On the heavier side with great balance and feel. Later batches tend to come from younger trees that then need a lot of drying and chemical treatment, etc. - such bokken are not always so durable at the end of such a process. We've had a couple of "younger" sunuke bokken come lighter and eventually splinter/break. For the older ones, dents are minimal to none and spinters are almost non-existent. No special treatment is needed, just a light topical oiling from time to time with an even lighter sanding even more rarely to keep any dents that might show up from getting worse (maybe once or twice a year - maybe a bit more depending on your skill). We do contact weapons work around four times a week - sometimes more - it's all no problem for this bokken. You can see our level of contact in this video so you can get a better idea of what kind of treatment this bokken recieves weekly. My partner in the video is using a one of Kim Taylor's hickory bokken.
All that said, two other elements remain:
- The better you are in your sword skills, the higher amount of contact you can make without risking great damage to your bokken.
- Bokken are really not meant to last a lifetime. They are tools meant to be abused (in some ways) and as a result, one should not really look to buying one bokken over one's lifetime but rather be prepared for buying several - as many as necessary.
Sure, you don't want one that's dangerous to use because its structural integrity is greatly lacking, but at the same time you can increase any "structural integrity" by cultivating greater skill AT THE SAME TIME that you realize that all bokken do damage and will have to be replaced eventually.
Just my experience,