Not a huge fan of Alpine units myself.
I've used Clarion, Alpine, Eclipse and Pioneer. I've personally found Alpine units to be the least accurate sounding, with an unnatural 'enhancement' of midbass frequencies that leads to an unnaturally 'bloated' style of sound. I've also found the user interfaces to be especially unintruitive and a right pain in the butt - at least on the higher end models with full active processors. They are also IMO way overpriced in terms of the features you get for your money.
I've found Clarion to be probably the most neutral and accurate, with Pioneer and Eclipse also quite nice.
Right now far as value for money goes I think Pioneer and Clarion are probably the best compromise between features, price and usability but that's just my personal opinion. Everyone is different
Yes with no local warranty, so if something goes wrong in 5 months time you have to pray that the seller still exists and is willing to pay out of their own pocket to replace the unit for you.
Last I checked Alpine do
not approve online sales (especially on ebay) and will not provide warranty support for any product not purchased through an authorised reseller. At least this was the case a year or so ago - could have changed since then, but I doubt it.
If you are willing to take the risk, then you can defiantely save a lot of money that way...but it's up to you to decide whether the risk is worth it for the amount of money you will save.