The clue is in the statement 390~450 lumens per meter, if fed with a constant current LED's should emit a constant amount of light. There are two basic ways of feeding a line of LED's.
One is to split the LED's into groups, often groups of 3, and place a resistor with each group to control current. This is very wasteful as the resistor just produces heat, but it is easy to power using a simple fixed voltage power supply often 12 volt. It is good enough for decoration, but not really what you want for general lighting. Because there is no current regulation as the LED's get further from the supply they get dimmer and dimmer, and also you need to use quite thick cable.
The other method again splitting into groups, but much larger groups, often 15 in a group, and this time the LED's are controlled with a current controller often PMW (pulse width modulated) with a variable supply voltage often 6 ~ 50 volt but a fixed current typical 320 mA, this is a lot less wasteful typical 100 lumen per watt, and the current controller auto compensates for volt drop and the voltage is a lot higher to start with so the wiring is a lot thinner.
With the former you can often run multiple power supplies in series to try and reduce the volt drop, but these would need to be positioned along the run so you end up with a mixture of low and extra low voltage wiring. With the latter again you can run multiple units and each unit will have it's own group of LED's but the "drivers" as the power supply for this type is called can all be together as there is no volt drop problem.
Note in the lighting industry they are not good at using correct names, read the spec do not rely on correct names. In the main the driver can be tweaked slightly and the current dropped a little so extending the LED life.
With the voltage power supply dropping voltage can make some LED's rather dim, so often those close are over driven and those away from power supply are under driven so those over driven may have a short life. LED's do produce heat and what they are mounted on does make a difference, they often have sticky backs to ensure they are held to some heat sink, this sticky back tends to fail causing over heating then LED failure if powered to their limit.
Using cheap LED's designed to run on 12 volt powered with 11 volt will likely last for years and look very good. And for decoration are no problem, but if being used to light an area the volt drop will mean too much light loss.
