The only way you benefit from the lab ray is if you trade pets on neo. The pet market isn't very interesting at all. If you go in the PC, you manage to get a REALLY good zap, you can probably trade for a good pet. But for money and neopoints, not worth it at all. The lab ray roughly gives a species/color change ~2 times a month for me, and I have two accounts with lab. Petpet lab is NOT profitable at ALL. You can't sell and detach ANY petpets that are zapped. As soon as you take the pet pet off it turns back into the original equipped petpet. The only way to benefit from this is if you get a avatar petpet zap and have it aged, but not in a profitable way that makes you money either.
considering the size main market malling requires these days malls take around a year or more to make back what was invested into them, and thats if you have a good spot, otherwise it can take longer...
For training i think so, you tend to get very high HP and very high strength after continous use, but the defence and level are usually low so it's best to get a high level before you start zapping so you can get burrow and berserk attack. For colours i think it's definitely worth it, you can get many colours only by labbing, plus a lot of colours that would cost a ridiculous amount more from using a paintbrush. Also if you get a rare colour on a species you dislike you can trade for one you prefer
I love the lab ray for pets - but it's a big waste for petpets. Profitable - no - but it is a great feature if you are into the pets. You can get stat increases and color zaps that you can't get any other way - such as Ice or MSP for Poogles. You can get LE pets from zaps as well.
Ough I dunno... Considering how much Lab Maps cost right now, and how low of a chance there is that you will be getting the colour that you want, I wouldn't jump in and say it's cost effective. There are very few colours that cost more than a mil, and I'm pretty sure the lab map is quite a bit over the 1 mil mark at the moment. But, if you don't care about your pet's stats, I guess it's 'fun' to zap pets for colours and species.