So far as the UK is concerned it would be good for us if Le Pen won. She is likely to be up against Macron in the 2nd round (unless Fillon makes a recovery - which he could, this is France after all). Macron is out to punish us for Brexit. Trump would be happy to deal with Le Pen - but not to the exclusion of Britain. Could be a good triumvirate, possibly.
I am quite sure that she will win the 1st round (and have been for some time) it all depends on how the Left splits and reforms to oust her and how many of Fillon's supporters move to her - assuming that Fillon is not in the run-off). French politics are very complicated and fluid. It is the 2nd round that counts, they get serious then.
I have placed a small bet on Le Pen winning, but it is money I am prepared to lose - I know how the French band together to prevent the 'wrong' person winning. The Left will all band together (if it is
Macron, which I expect) and would out-vote her unless the Right vote against Macron. Very interesting - this is where I get my money's worth out of the odd, small bet on politics. :)