I would not have said no difference between them. But the differences could possibly be described as minimal. Many people might not see the difference because they 'look' identical. But internally the engine in Pro is fine-tuned more. It connects to 5 peers compared to Basic's 3, which really benefits for searching rarer files, not the common files. Pro has the ability to download from a couple more sources per download than Basic but only if you have a high bandwidth connection & are well set up & find enough free sources.

But some people suggest being a pro user is more of a donation to the continued development of LW.

If you have doubts, then simply use the free LW Basic. Particularly if you're only after commonly found files.