Hi folks,
For those of you who are still deciding between these two tests, I'd suggest taking CELPIP for several reasons.
First, CELPIP is one-day one-shot exam, meaning all four components (LRWS) are on the same day in one sitting.
Second, I've taken both tests and noticed that improving the writing score in IELTS is way more difficult than doing it in CELPIP. Perhaps, due to numerous factors such as illegible handwriting, spelling errors, punctuation errors etc. Additionally, while responding to the time-constrained writing tasks with a pencil/pen on a paper might leave us to figure and correct the errors, which is again both time-consuming and tricky to do it on paper. On the other hand, CELPIP detects spelling errors and even suggests a list of possible choices for an incorrectly spelled word. For example, when you write 'youre' in CELPIP it shows a spelling error and if you further right click, it suggests you two choices to chose from: you're and your. Further, you could even copy and paste the text and need not mention deleting or any other editing function is a lot easier on a computer than on a paper. I could score 6.5 in writing with my 2 attempts in IELTS but with CELPIP in 1 go, I got 10 in writing.
However, speaking part in CELPIP could be either good or bad depending on how much you're comfortable speaking to a computer screen or to an imaginary person. Personally, I'm more comfortable to speak to the expressionless computer and imagining it as a listener who could be my family member, a close friend, boss or any other person. Another major difference in the speaking part of CELPIP and IELTS is that in CELPIP you've to decide the right tone/formality of your speech for each task but it could be practiced easily.
Good luck!