My pioneer thingy(XDJ-R1) is ball park, but rarely does matching them get them locked, handy to get close, but you really do need to use your ears to get them in proper time.
On a software side, if playing around just on my puter, I have always used the free version of VDJ. People call it a joke, but in my experience whilst it almost always halves the bpm to sit in the 85-87 BPM range, it is spot on every time. If I feel lazy or I just want to work out how some mixes sound, I know I can go into that software, click sync and both songs will 99.99% of the time be matched perfectly on bpms. It does struggle a little with the beat grid though, so if you wanted to mix using the sync button to lock your tunes while playing back, it will never get them laying together in unison where you want them to be, they will be the same speed, but due to the crappy beat grids, will mostly sound like train wrecks.
I use it though just to get the speeds the same, then everything else in on me and my ears to get the right starting point, and get the tunes playing together matched properly, by adjusting them in the normal manner, by using your ears. But using that software, I am 100% confident, that when I hear them locked in the cans, they are going to stay that way for the whole mix.
I prefer to try and do the work though, and when having fun I like the challenge of not relying on software to do anything other than playing my tunes, I can match the speeds fairly competently, and can record an hour or so(sometimes haha) without it sounding too offensive to another DJ's ears.
Like everyone has said, try to use your ears, you wont get taken seriously with the headz in the DJ'ing community unless you can do that, but if looking for a software solution to get the speeds right(not much else though without some editing of beat grids, which just sounds like a massive ball ache to me), I would heartily reccomend VDJ for this purpose. You are still gong to have to start the tunes in the right places, and manully jog them to get them sitting together perfectly, but you will never have to worry about the speeds of your tunes being wrong.
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Why do you need a bpm counter? Use your ears m9
Whilst I understand the indignation with Technology in the DJ'ing community, and whilst I agree that anyone pursuing the dream in any professional capacity should be able to do this, to be out playing and getting paid, the fact is, not everyone is looking to be playing out at a big club, or making a career out of DJ'ing.
For some of these people, all they want to do is sit at home and mix some tunes together without it sounding like shit. By using these tools, people can actually do that nowadays, and produce mixes for themselves to listen to and enjoy, rather than sitting there and making a sonic mess by fucking up every mix they try.
Depends on what function you are looking to fill when Mixing.
Professionally, agree wholeheartedly, get your shit together and learn to be a dj proper.
Recreationally, do whatever you want to do, that gets you from point A to Point B, that you feel good with. If you want to learn proper, learn proper, if you just want to sling a mix together without learning, get some tools to assist you. Some people are just not good enough without the tools to do a good job on a mix.