It depends entirely on the pairs and settigns you are running. I run over 50 pairs on my custom settigns, and have made 6.7btc or 228% in profits since 24th April.
You have to put some trust in the developer, but not a lot. I run the bot on a VPS 24/7, and haven't updated it in a few months. The developer NEVER has access to your Poloniex API Secret-key, and even if he did, withdrawals are disabled for the keys, always.
There used to be a trial period, but peeps were abusing it, so it was removed like 5 months ago. There are almost 600 satisfied customers though, if you'd like to have a chat with any of them. The bot also has a 15 day money-back guarantee on the terms laid out in the bitcointalk opening post...