Hi Bonzhara,
Welcome to the forum!
In Russia, the cards are red (j/k!), and they're called temporary and Permanent residency permits (TRP and PRP). Work permits don't become these automatically; there's a whole process, with quotas and exceptions to quotas- lots of residency permits info is available on this forum.
As for the plusses and minuses of your work permit (rabochaya visa):
Plusses:
One of the longest non-immigrant visas; you can stay in the country for a year
You can renew this visa in-ountry, provided you stick with the same employer
Minuses:
You're tied to the employer, and if as I assume you're working for a TEFL school, you'll be getting paid less than you would teaching privately, even after accounting for taxes. It's not as bad as our H1B employers who dangle prospective citizenship in front of the Indian and East European programmers at Facebook and Google to overwork them for low pay, but the employer here kind of has you by the balls since he controls your legal status in the country
If you switch employers, you have to leave the country to get a new visa. You can request a work visa invitation letter from a new employer while still in country, which if you time it right (4-6 weeks processing) could allow you to leave with the physical letter in hand (originals are required) and then apply immediately for your new visa upon arrival in the UK.
This is the other big downside (I think you mentioned being from the UK): because of reciprocity or whatever, as a Brit you can't just zip over to a neighboring country for a visa run, as we Americans can do. You'll have to go back to the UK to apply for your new visa, which I imagine greatly increases the cost of your decision to switch employers.
Of course, most of these downsides exist if you come on any other visa as well (tourist, "business," homestay, academic), and technically it's illegal to work on those visas, so in this sense my list is not so much about downsides as it is about unforseen factors to consider before trekking over here.
I wish you much Harmony & Prosperity as you prepare for this life-altering trip abroad to the land of hard souls, frigid weather, and hot women!
I am fascinated by Russia, this country with frigid weather, hard souls, and hot girls!