I have several of these Sandisk SD-plus cards (a few 1GB, 8GB, and now the 4GB version), and they are excellent. The build quality is very good - no danger of them breaking at the hinge when using them as USB drives (I've been using them as such for at least a year and they're still fine). And they are very reliable cards.
My only problem is with the recently purchased 4GB version. This is the first time one of these cards has malfunctioned, frequently appearing via two of my three USB ports as having 0 byes when it's clearly a 4GB card with over 1GB of files (if anyone knows of a reason my computer may be at fault here, do let me know!).
My concern is compounded - though perhaps unfairly - by the fact that this card was purchased from am Amazon Seller (Flashsuperstore) and arrived in padded envelopes and a small transparent plastic case - i.e., this was NOT a retail-packaged card (see my customer photo). Now, I'm sure it's fine. But having a product arrive without its retail packaging allows for a number of problems, and it may be best to check with the sellers before you purchase such cards to check this kind of thing.