Okay great, so 10,000 times smaller hole size, what does this really equate to?
See the graphic above  which is a correct comparative scale, so you can see it's obvious why 1 micron and 0.5 micron systems do not reject much of anything, much less should they be saying they “purify” water. 

“Purified water” should mean that there is almost nothing in the water but the actual H2O molecules, which is clearly not the case with 0.5 or 1 micron systems.  Look at it this way, if you filter salty/brackish water with a 0.5 or 1 micron filter, your output water will have the same ​salinity as the source. In RO, you would only have pure water output - no salts.

What about filters that include a ultraviolet light (UV) stage? 
Yes, a UV stage will kill bacteria, viruses, etc., so those things won't make you immediately sick, but what about all those other toxins that can pass through with 0.5 and 1 micron systems? Heavy metals, pesticides, forever chemicals (PFOA's), etc, etc. The On the Go RO system includes a UV stage as a backstop to the RO inherent quality. 

If you are going to pay for a water purification system, why not make sure that it's doing the whole job and not stopping at less than 10% purification. 

On The Go RO has put together a portable 4 stage Reverse Osmosis system that actually does purify water, giving you confidence in your water from almost any water source. Additionally, our system is designed to increase the water output and significantly extend the life of the RO membrane - saving you money, with indicator lights letting you know when it's time to replace the pre-filter or membrane (vs. industry standard of no indication, only X months).