Cloyster worth keeping?

It isn't really valuable unless you don't have a Lapras or even a Dewgong. Sure it could beat dragonite easy because of the type advantage, but to put 70k+ dust into it... i don't think it makes a lot of sense.

I would just cuz I think cloyster. It will own dragonite and you're always guna be working your type advantages anyways.

Powering it up to level 29 is only going to give you ~1700 cp. Might try taking it up just to ~1400 to ~1500 and try it for training ally gyms.

https://pokemongo.gamepress.gg/cpcalc#/
You can check here to see exactly how much candy and stardust you will need and how big it will be.

It's never going to be a defender. If you are level 28 already (I assume so if you can power up to 29.5) odds are you will catch a well powered up shellder and evolve a higher CP cloyster with the same moves and no dust spent: IV doesn;t really matter if you aren;t going to power up to max and with a mon like Cloyster that has high attack stack but very weak on HP, the ideal gym leveller is probably a 0-15-15 IV anyway! I got one with 1492cp and its actually still pretty lame prestiging against dragons - if you miss one dodge against the charge move its all over. A good Wigglytuff with Pound/Play Rough is much better, especially against dragons without steel wing.

f*ck the meta, man...

I would power up (and i will do so with mine) cause I love cloyster. He's got such a bad ass appearance with all those spikes and the evil smile... I have one 77,5% at 1550 CP and he already destroys dragonites (provided you dogde well) imagine what a 95% lvl 30 could do...

Cloyster is great against dragonites, you just have to dodge because they have no HP.

You don't need to power him up all the way, like others have said, powering it up to 1400 or so will be enough to take down 3000 CP Dragonites or more.

Cloyster is fun and fares really well against dragonite. The only downside is the low HP, so you likely won't be able to take down 2 high CP dragonites with 1 cloyster.

It's sort of up to you. If you do enjoy some variety and it makes the game more fun for you (it does for me), go for it. But based purely on mathematics, the Stardust will always be better spent on the top 10 CP pokemons...