The 501B is a fine light , ok it not as heavy a build as other lights , but you dont always need bulk ...
Mine is XR-E R2 and runs fine [ pill is wrapped in Al-foil to heatsink into the body better ] but mine handles the XR-E just fine [ up to 1.7A @ the tail ] and have never had an issue with heat .
If you just dont like the look of it , I can see that , and the 501 is not a good choice for MC-E / SSC-P7 / SST or XM-L ..
Anything else though , should be fine .. I like my 501B for the reason its lighter and smaller than other 18650 hosts , and in XR-E R2 it throws fine and is a very nice flashlight .
The only issue I have had is the clicky switch, it may need a little work to make it 100% ... Often the switch boot is to tight a fit and presses down on the switch , and you may need to trim the switch boot a little .. [ THe rubber boot on the end of the light ]
Oh man ??? Where was my Email ??? Just kidding !!
Seriously , if 5 lights are sent out for review , then that should give us a better idea of the product , especially if everyone writes a review ...
Funny that , a ways back a manufacturer sent out a whole bunch of batteries for testing - review and I never saw more than one review as a result [ yeah , I was the only one to post a review ] , for the manufacturer . [ A rather poor result ] . But its up to the sponsor , they pick who they are interested in doing the review , etc .
And then its up to the individual to decide if the terms are acceptable ..
Sounds like the 501 is invoking a bit of negative feeling ?