The Improved Meyer Lemon tree is the same thing as the Meyer Lemon tree, only this one is a improved version, making bigger Lemons that have a longer shelf life. This grafted specimen is cold hardy down to 10 degrees farenheit, making it slightly more cold hardy than the standard Meyer Lemon tree.  The Improved Meyer Lemon tree does well in full sun and can be planted in partially shaded areas also, still being able to fruit. No companion is needed for pollination and it wont cross pollinate other citrus plants either. Expect large yields of lemons from this particular specimen, they tend to produce very heavy. (USDA Zones 8-11)