My take on the 510 manual mega's (after about 2 weeks of regular use) is: They're
great. They definitely last longer than the standard titan
batteries. If I have 2 or 3 charged up when I leave the house, I don't really need to bring a charger with me. I'm glad I decided to go ahead and check them out because I was getting sick of charging up/switching out
batteries all day. Drawbacks? They cost a lot. They're also huge--if you care about such things. But a 510 with mega attached is still a bit shorter than an 801. If battery life is your biggest beef with the 510, I'd definitely give these monsters a try. Don't know how well they hold up with heavy use but I guess I'll be finding that out down the road.