I have the TMC Grobeam 500 in my tank, my experience is mixed with them.
The tank is a Juwel bow fronted 260 litre (68 US Gal) which has been through the original dim Juwel T8 which got upgraded to the Arcadia i-bar T5 (which died) and is now on the Juwel T5 hi-lite lighting bar. This has 2x54W T5 tubes, one daylight spectrum and one marine white to give a non-yellowish colour which looks good to me.
I added a pair of TMC Grobeam 500 to the tank to fill in with some more light about 12 months ago.
First the good;
1) The light is quite well directed to the substrate and doesn't light the room instead of the tank like the T5s
2) There is a nice shimmer from the LED lamps
Now the not so good;
1) The first set failed after about 6 months because the water seals simply didn't work, water got into the lamp units and rotted them. Upon inspection the water seal design seemed less effective than I would expect. The design of the replacement units is different so this may not happen again.
2) It took months to get a replacement set from the distributor, my LFS were very frustrated with TMC and the distributor and apologised to me many times, just glad I wasn't relying on TMC for light in the tank or my plants would all be dead
3) Within a week of receiving the replacement set the little AC/DC PSU lost an output meaning I had one Grobeam not two, these seem to be a cheap Chinese unit, once out of warranty I have an alternative PSU which I expect to last a reasonable time.
4) The replacement set has lost one LED already, these will be going back under the EU 2 year warranty requirement, so far the lifetime I have experienced is no better than the T5 tubes
5) The light from these units just is not very bright, they are not in the same league as the the 2x54W T5 and I would expect to need a lot more than 6 of them to get that much light, I suggest you look at some of the newer design higher light output units out there instead, LED tech has come a long way since the vintage of the emitters in the Grobeam.