Suppose on my friend, lol. I'm not saying anything against manzi or any other wood. It may or not stain your water but that's not a big deal...it'll depend on your BN's preferences for grazing & if you can make a couple caves. Maybe Mopani or Malaysian instead of manzi? Manzi tends to be thinner sticks. Mopani seems very hard & smoother on it's upper tan surface. I prefer Malaysian slightly...but there are other woods too..soft woods like pine are not the best choice. They tend to take a longer time to become water saturated & sink . I have a nice piece of manzi sitting on my patio I've tried soaking a few times but thinner wood also dries out faster...
There really isn't just 1 right answer, experiment! & see what works for your tank & fish...it'll cost maybe $8 or so...don't be so cheap that you miss a few easy ways to make your fish happier & your tank prettier. Wood & plants often can last for many years...trivial in the long term...