He hasn't got a poor record before last season. Leicester plucked him from the non-league because he had a fantastic scoring record at that level - 58 goals in 73 games.
He struggled in his first year in the Championship as he adjusted to the new level but the following season he did OK - not setting the world alight but he got 16 goals in the league.
The same pattern happened in the Premier League, struggled in his first season, did very well last year.
The fact is we don't know how he'll do in the next few years, he's not got a long history of scoring goals at the top level simply because he's not been at the top level for long enough, but he has scored a reasonable number of goals at every level he's played at.
It's rare for a player to make it so late in his career so he's a bit of an unknown quality, I doubt he'll have another season quite that good again but he is a goal scorer and we could do with one. But yes, if he's going to dick around then he can do one, there are players out there with a longer, proven track record who would probably be more expensive but are less of a gamble.