Looking to buy CSPX to hold long term and am deciding on which brokerage/robo to use. Should I buy it through Kristal.AI (free for first 50k) or IB since I intend to purchase other ETFs/stocks too?

I'm using IB now to buy the S&P500 etf, but i opted for VUSD instead of CSPX (not much difference either way). Definitely go for IB if you are holding "long-term". You can google both brokerage's pricing, forex spread and ease of usage, clear terms and conditions etc and will realise that in the long-term, IB is much better. Reasons i'll list below.

To buy CSPX etf on Kristal, you have to pay for the unit GAV price, which is currently at US$323.16. Note that this price indication is a delayed price for 2-3days. Currency conversion on kristal seems ok, but incomparable to IB forex spread which is near spot rate. Also, Kristal uses AUM to calculate its fees, while you pay your fees as per trade for IB which is usually only ~US$1, even if it's a LSE etf (opt for tiered pricing and not fixed). Imagine you hold long term for 15years. I'm pretty sure your AUM would've exceeded $50k and you can calculate simply the fees you'd pay annually, and the money lose out due to currency conversion. ALso, IB has good market data reports and steady platform to track any stock/etf you want to trade. Do consider if those will be important or aid your investment when you become more knowledgeable in investing.

In simple words, Kristal is a robo-advisor and IB is a brokerage. With hidden fees in robos, there's no way your returns will beat out IB.​​​

I'll personally go with IB