I bought one from penrithsurvival and it is ok:shrug: I also have a 18MM green sphere from b@rt over in the marketplace it is much brighter than the disc in the tritium torches from penrithsurvival.
Put that sphere into a shallow reflector and it easily enough to read by or navigate around the house at night. Photonfanatic can make you a custom body and reflector they are not cheap but very nice.
Best bang for the buck? Get a 18MM green sphere from b@rt, some norland from rockettomato and glue it into a reflector. You can use other glue but the norland is supurb.
This picture is b@rts orange sphere compared to the penrith beta-light. The green sphere is MUCH brighter
White 15mm sphere glued into a reflector compared to 4x20 vial glued in a reflector