"VU meter" implies a certain set of ballistics (ie: how fast does a meter respond). This is standardized; if a project specifies the use of a VU meter, any real VU meter can be used and it's up to you to pick one that best matches your case design, your budget and/or whatever you happen to have lying around. The trouble is that lots of cheap meters are also labeled 'VU' (as that's what consumers had come to expect), so if you have a random meter you can't be sure that it actually meets the spec.
Whether you actually need the ballistics to be true really depends on your own workflow. Some don't use the meters as more than glorified 'signal present'-indicators; others find them very valuable.
This has been discussed quite a few times, but those threads are hard to find if you don't know to add the word 'ballistics' to your search. Here are a few which you may find useful:
On the VU meter standard:
http://www.groupdiy.com/index.php?topic=245.0
http://www.groupdiy.com/index.php?topic=27307.0
http://www.groupdiy.com/index.php?topic=21604.0
About dB, VU and metering:
http://www.groupdiy.com/index.php?topic=28025.0
VU meters vs other meters:
http://www.groupdiy.com/index.php?topic=22899.0
http://www.groupdiy.com/index.php?topic=11116.0
http://www.groupdiy.com/index.php?topic=1996.0
Testing VU meters:
http://www.groupdiy.com/index.php?topic=14407.0
HTH,
JDB.
[VU-metah-META, anyone?]