I've been experimenting with this off and on for the past year now. My conclusion seems to be that prostate massage is the most effective "alternative method" to deal with BPH, but there are some things to consider.
As Susie notes there is a big difference between the type of prostate massage that helps and the type you get with the Aneros/Nexus/whatever prostate toys. To get any benefit I or my wife has to lean into the prostate pretty hard and make sure that most of the posterior surface is covered. If you have BPH of any significance then you'll know that your prostate is much bigger than the oft-cited "size of a walnut" and the heads on even the larger prostate massage toys aren't big enough, so even if you could put enough pressure on it it would be hard to ensure coverage. I think my wife's fist up there would be very effective, but we haven't gotten there yet. Another point on the pressure is that the sensations can be very intense. If done right, with lots of foreplay and sexual excitement and slow work up they can be nice, but you do need to get used to them. You'll be squeezing out prostatic fluid even if you aren't aroused, so if all you see is precum or nothing than you're not doing it right.
After a session of prostate massage I notice improvements of about 2-3 mL/second in the flow rate, and generally a reduction in the amount of dribbles at the end and "spray" of urine. It takes a couple of hours for the improvements to show, and they usually start to go away slowly after a day, with the maximum improvement I've seen being about 2.5 days. One thing I do note is that there seems to be more brief interruptions in the flow in the first 6-12 hours after a massage.
I'm not sure about safety here. To get this to work you do need to use significant pressure across the whole posterior prostate, though not enough to cause bruising. I don't know what the effects are, nor do I know of any long term studies on the safety. One thing I can say is be very careful with this if you have active bacterial prostatitis. It will hurt like hell and you probably will spike a fever afterwards, both of which have led me to take a more hands-off approach if/when I have my next round of prostatitis.
Will I continue this (therapeutically, definitely planning on continuing prostate play erotically)? Don't know. If so how often? Again, don't know. Daily or every other day seems like it might be a bit too often, but I'm not sure.